Error code 20

I am a woman who is pretty house/mechanically handy (esp. having been an electronics and computer tech in the Navy some years back), and today, I was able to fix this issue on my 1-year old Frigidaire Affinity front-loader. The issue is, in fact, a clogged drain pump. It happens because there is a small white basket located inside the pump and drain mechanism, and it collects debris and things like hair, etc. as it drains the dirty water from your machine.
Here is what you'll have to do, and it's a pain (and time consuming), but it will save you several hundred bucks for a service call. I was able to accomplish the whole job with a mid-sized phillipshead screwdriver, a pair of needle-nose pliers, a flashlight (a must!) an adjustable wrench, a two-by-four piece of wood and some paint cans (to prop up the machine to make it easier to work on), a bunch of towels (to clean up the water that leaks out of the drain hoses and pump), a couple of hours--and glasses of wine to keep me from kicking the thing apart.
On the newer models of this machine, there is no bottom front access panel. This is what makes your job a pain in the you-know-what. You can reach the pump through the back round access panel (although it's a tight fit), but the problem is the pump contains a series of clamps, the most notable of which is a screw-clamp the assemblers have assembled with the screw-tightener facing toward the front of the machine. You might be able to loosen it enough with a pair of needle nose pliers from the back access panel area, but if you cannot, see my additional info below.
Try this first:
1. Once you UNPLUG THE ELECTRICAL PLUG (a little CYA for the dense), put the paint cans under the back corners of the machine. This is really going to help you reach the area you have to work in--otherwise you will wreck your neck and back. You'll then remove the smaller round access panel from the back, to see the pump located beneath the wash drum and belt drive. It's black, rubber, and attached to a series of drain hoses and the motor with a few clamps (mostly green in color on my machine). Assuming you are able to reach the pump and loosen the screw clamp coming from the main tub drain (it's waaaay behind the tub and a complete pain to get to--either from the front OR the back, so try first to loosen the screw from behind with some needle nose pliers).
2. Next, you need to remove all the drain clamps and hoses and unscrew the motor from the bottom baseplate of the washing machine. You'll need to also unclip the electrical line from the motor and place it up and out of the way (I just put it in the belt) so it won't get wet. JUST DON'T FORGET TO RETURN IT TO THE MOTOR DURING REASSEMBLY. The screws are located on either side of the motor casing and are black, so the flashlight comes in handy. Unscrewing the motor from the baseplate first makes removing and replacing the clamps much easier.
3. Remove the black pump and drain mechanism and the motor. Make sure there is nothing in the motor housing (just in case). You'll note that once you dump the collected water from the pump, there should be a white plastic round basket with holes inside the pump unit. It might be set into the large mouth of the pump, but it might have also been forced into the large open body of the pump over time. It also might be so clogged with stuff that it is unrecognizable at first, but you need to pull it out, clean it out, and wash the whole unit out with bleach water or CLR and water. As an aside, you'll probably want to do the same to the inside and outside grey drain hoses while you're at it. You can remove the inside grey drain hose by unscrewing it at the upper left exit panel, lifting the plastic catch up off the access panel, and unclipping it from inside holding clips in the machine. I also, as a precaution, took a wire hanger and ran it through to make sure nothing was caught in either of them (I have three teenagers, so you never know).
4. Once you clean the whole unit out, replace the white filter basket by placing it into the large mouth of the pump. It ought to fit in that recess perfectly. Also, ***note this***: before you replace the pump, go ahead and replace the grey inside drain hose onto the pump. It's much easier to clamp on while the pump/motor unit is still outside of the machine housing than once you've put it back in!
5. Now is the hard part! You have to replace the remaining clamps and hose lines. A ****second note****: I decided to go ahead and remove the screw-clamp and place it backwards so that I could reattach and tighten it from behind next time (having had to remove the front panel and electrical work to access it in the first place....see note below). I won't lie to you--it's a complete PITA. You have to make sure the lip of the pump opening is set high enough to that part of the washdrum that when you tighten it back on, it is water-tight and cannot slip back off. I used the needle nose pliers to help push it up further. It also is pretty hard to reach, and the belt-drive housing has a sharp edge to it that can gouge your arm while you're doing it. Anyhow, replace the screw-clamp part of the pump first, and it will make it easier to do the rest, as it will hold the pump in place. You may need to twist it tight as much as possible by hand, then use a phillipshead and/or needle nose pliers to tighten it the rest of the way. It ought to be tight enough that if you pull on the black rubber drain unit, it won't cause that part to slip back off. Next, you need to replace the upper left smaller hose-connection (next to the large opening of the pump with the screw-clamp). You'll probably want to push the clamp up onto the white opening, return the rubber pump connector to it, and then reclamp down (much easier than trying to clamp it from the bottom). It's a pain because there's only so much room for your hands, and you cannot really get the clamp on straight at that angle without a lot of patience.
6. Once you've replaced the pump lines, go ahead and screw the motor back onto the bottom of the machine. Also, DON'T forget to re-attach the electrical line to the motor. Replace the outer grey hose with its respective clamp, screw the back access panel back in, and you're ready to plug her back in and wash some clothes!
****A note about the screw-clamp****, incase you cannot reach it from the back. You are going to have to undo it from the front, which will require you to also do the following:
1. Remove the top of the machine by unscrewing the two screws on the upper back of the machine. Once you do this, you will see the electrical wires for the control panel. DON'T UNDO ANYTHING. It will appear you might have to in order to take off the front panel, but you won't.
2. Next, take the two-by-four or some paint cans and place them under the front of the machine to help prop it up so you can unscrew the four bottom screws from the front panel. It's not going to come off just by doing that, so you have to take out the detergent tray, where you'll then see two screws inside the tray crevice and you'll have to take them out. Set those two aside elsewhere--they are longer than the other screws and you'll want to make sure you put them back in the right place. On the top front edge of the washer's control panel there should be two screws on either side securing the plastic control panel to the front of the washer. Unscrew those. You should now see the remaining screws holding the front panel on. Unscrew those as well.
3. Next, open the front door of the washer and you'll see a little grey set of plugs that look sort of like USB ports on the right-hand side. There are two screws holding it on--undo those. You should now be able to pull the front panel out just enough to reach that screw-clamp in the front to unscrew it. Once you do, go ahead and replace all the screws and parts of the front and top you've undone. You'll want to do that before you proceed to taking out the pump and cleaning it, so that you can remember how to do it more easily.
A last note: When you remove the top panel of the washing machine, you will see some papers taped in there with funny drawings (in case you are a novice and not familiar with schematics). PLEASE LEAVE THEM THERE! They are the schematics for the circuitry of your machine, and God forbid you one day have to have THAT worked on, your repair person will definitely need them.
Good luck, and hope this will help you!

Knexsen's solution worked for me, but being lazy I took a shortcut. Instead of completely disconnecting everything from the black rubber assembly that contains the filter basket, I just disconnected it from the pump. Within the main body of the assembly I was able to work the filter basket around until the top of the basket, which is open, was visible through the opening that leads to the pump. With a pair of needlenose I was able to remove the object blocking the filter, which in my case was a sock (and to think, all these years we've been blaming dryers!).

Speaking of dryers, mine is stacked on top of my washer, but I was able to safely tip the whole works forward (good suggestion, that) with the use of brace between the dryer and the nearest wall.

I was able to fix my machine using Knexsen's solution and, like Keith_Mann, I didn't disconnect the whole black rubber assembly. I disconnected the pump from the black rubber assembly and was able to remove the filter basket from it. I found a small sock, underwear, and some change! It's a wonder how this thing drained ANY water! The basket was a pain in the a$$ to get back into the black rubber assembly, but with some pliers I was able to stretch the opening over the lip of the basket and get it into the proper postition. A few recommendations:
1) Wear long sleeves - I didn't, and when I was working through the back panel, trying to work the basket back in, and also connecting back the pump and hoses, my forearms got cut up from rubbing against the edge of the back panel. Nothing major, but would have liked not to draw blood on this project.
2) Have lots of patience - Especially when connecting back the hoses with the clips.

Thanks guys, the machine works great after the fix!

I ended up calling a repair service, and they cleared out the drain. There were several small pieces of fabric and a piece of wire clogging it. The repair man said the most common cause of the E20 error is just the drain having something blocking it.

You need to clean out your outlet filter; this needs to be done periodically - according to your usage. If this does not solve your problem check out your outlet pump. Plug off the wall first before you do the jobs. The machine will not drain if the outlet is clogged. Refer to your manual; if you cant find yours.........

These responses are great and they really helped me. I wanted to add my experience into the mix in case it helps anyone else.
Here are the tools that I needed:

• headlamp for peering in the washer
• large phillips head screwdriver
• small ratchet with M7 socket for the screw clamp

I had a fairly tight space in which to work. I have a stacking set and they are between a big sink and a piece of wall. I had to remove the dryer from the top. There are two screws in the front bottom of the dryer that secure it to the washer. Then I slid it over on top of the sink.
I pulled the washer forward and shook it around. It still had a good bit of water in it, but I was able to get it to drain by running the spin cycle several times and shaking the washer around. I was watching the drain line and it just trickled out, but eventually I got it all.
Once I got into the back panel I decided to try to just remove the filter basket. I opened the screw clamp and left the others alone. The screw on the screw clamp was an M7 and with a small ratchet it came off quite easily. If all you have is needlenose pliers, they will work, but you will be there a while! I was able to remove the black rubber bellows and work the basket out without too much trouble. It was packed! Fabric, leaves, coins, bobby pins, paper clips, and unknown solids. I pushed it all out with a screwdriver and rinsed it. Getting it back into the bellows was a little tricky, but the rubber is very pliable and I was able to work it down without too much effort. I tightened the screw clamp back up and closed up the washer. It drains great now!
I am a mechanical engineer and I can tell you that the clamps are different for a reason. The green spring clamps are only to be undone when you are changing out the pump. To clean the filter basket you should only need to remove the screw clamp. Another person suggested going through the bottom of the machine, which I didn't have room to do in my laundry room. That might be a good solution and then you don't even have to remove the back panel.
Thanks to all the posters who put in the original responses. This was a big help for me.

The exact problem I was having and by cleaning out the filter the problem was solved. Two recommendations:
1) Wear gloves. The inside edge of the opening can be very sharp.
2) Depending on the room you have to work with I disconnected the hoses and laid the washer on its back. Mine has a bottom opening that made it a lot easier to access the clamps. It also eliminated having to remove the pump.