I can't remember how to format the memory card on my camera - I've searched all the functions, but can't remember how to do it!

Put the memory card in your camera and format the memory card using the options in the camera menu. Do not format the card on your computer. Check the camera's manual how to format your memory card.
Remember that if you format a memory card, all data on that card will be lost.

Have you actually formatted the card in the camera ? Just copying the photos does not remove them from the card

I've uploaded the user manual here UManual.
I think page 45 will help. Also look at formatting a memory card.

There is a tab on the memory card so you will you need to remove it from the camera and change the position of this tab to "unlock" it. DO NOT format the card until you've BACKED UP your files from it (typically to a PC or USB drive (stick or external hard drive).

Sounds like you're yanking the card or card reader out without using the "safely remove hardware" function on your computer. This habit can corrupt the card (as you've found out).

This error message means that the card is corrupted or formatted for another digital camera. Turn off the camera. Insert a new card or format the card.
Try to format the memmory card using a card reader and the PC this should solve your problem if not you have to replace the memmory card.

Without knowing the camera make and model I can only suggest you check your owners manual on how to format your memory card, your manual may also call it initialize.
I'm also going to include a diagram that shows the SD sliding lock, if this lock is in the lock position a whole sea of problems can "pop" up. the lock function is there top protect pictures or files on the card from being deleted by mistake. However sometimes these annoying little trouble makers get pulled down into the lock position.
Here is the diagram. Remember check the lock and then format/initialize your memory card also after each time you download your images from the camera or the optional card reader you must format the memory card to have the camera properly function with the memory card.

Hope this helps have fun with your camera

Yes, memory card is sort of a generic term due to the amount of different cards used in today's digital cameras. It appears that the manufactures are changing the card type and size to fit their smaller cameras. If the camera is working properly the only reason to buy another camera is to upgrade to bigger, faster and more functions. Your memory card should be available if you want another. Remember to format (initialize) the new card AND the old or original card you should be formatting not just deleting the images. Happy Holidays from Robert in Canada

Hi,
You just need to format the memory card. And make sure that you are in memory card option for the picture storage when you take pictures.
Formatting the memory card This function will format the memory card and will erase all files in memory including files that have been protected. Note: Once formatted all the images stored in the memory will be erased. This process is irreversible. Please download all images to the PC before formatting the card. 1. Touch the icon (arrow down) function area until you see the “Format” option.
2.Touch the icon (memory card drawing/picture) function area to enter the Format menu.
3.Touch the icon (arrow left) function area to select OK/Cancel.
4.Press the Menu/OK button to confirm.
5.A Format message will appear on the LCD. FORMAT?
YES NO 6.Touch the icon (arrow right) or (Arrow left) function area to select Yes or No.

Did you use the camera to format the card before you shot any pictures. If not, the camera can't use the card and used its own memory to store the photos. Use the camera to format the card, then the camera can continue to shoot more photos and store them on the card. When you download them to the computer, remember to get the one from the camera too.