Quantaray 28-90 mm f/3.5-5.6 af macro telephoto lens for canon

Quantaray makes lenses with many different mounts. If the lens has a Canon EF mount then it will fit your camera. If it has another mount, Nikon for example, then it will not fit your camera.

Sigma makes their lenses with a variety of camera mounts. If you get the lens with a Canon mount then yes, it will fit any EOS Rebel camera body. A lens with a Pentax mount, for example, will not fit a Canon camera.

The lens is a manual focus lens. It doesn't matter which mode you have the camera in, you'll still have to focus it yourself.

The older lenses will work with the Canon digital cameras, but they will be manual focus and you will need an adapter. The adapters are available at camera shops like B&H. I use some older lenses for macro.

The Nikon D40 requires the use of AF-S/AF-I lenses. Here is a chart of lens compatibility for Nikon SLRs:

Nikonian.org

With right adapters it should fit in any camera. At least Canon, Nikon, Minolta, Pentax. The adapters are 10-20$ each and easy to fit in the lense.

There is a website devoted to Err99: http://www.richardsnotes.org/archives/2005/04/29/50mm-lens-contact-points/

I have a Quantaray 100-300 which also displays an Err99 when used in automatic mode. The only way I can use this lens is in AV mode and select the widest aperture.

It will not focus on anything closer than 5 feet.

(From Sigma lens literature) Capable of macro photography, this lens has a 1:2 maximum close-up magnification at the 300 mm focal length. It's the ideal high performance lens for portraits, sports photography, nature photography, and other types of photography that frequently use the telephoto range. It also has a switch for changeover to macro photography at focal lengths between 200mm and 300mm with a maximum close-up magnification from 1:2.9 to 1:2. The minimum focusing distance is 1.5m / 59 in. at all zoom settings.

Your camera is only compatable with AFS-type lenses because it has no screw-drive motor.  You can only use AFS Nikkors and Sigma HSM lenses (the lens actually has a motor inside).  You were misinformed.  Bring the lens back and ask for a refund. Take that money and purchase a compatable lens somewhere else.