"Err 99" issue

I recently got a Rebel XT (8mp 350D)
My Canon 35-80 I got with my EOS 10S film camera works just fine. The Quantaray 70-300 I got kept giving me "err 99"

I assumed it was due to the fact that it was an older "off" brand. I went to my local camera shop and got a brand new Tamron 70-300 because I liked the 6 year warranty. It does the "err 99" thing as well.

Is there a problem with the lens?...my camera? Can I only use Canon lenses?

Any input would be most helpful!

Thanks in advance,
Mark

Have you tried cleaning the contacts on the lens ring in the body.

I understand you should not get Err 99 with any Canon EF lens. Something is wrong -- if cleaning the contacts does not fix it then I believe something is damaged -- physically or electronically.
You may get Err 99 with any "off brand" lens - I got it with my old Sigma 170-500 (I sold it, but it probably could have been re-chipped)

I don't get the error with my canon lens.
I got it with an older Quantaray, so I bought a brand new Tamron 70-300 di LD, and got the same error message with the brand new lens.

If this camera will only work with Canon lenses I'm going to sell it and buy a Nikon.

ERR99 can happen with any lens Canon included. Search on the forum for ERR99 and you’ll get a bunch of threads. It’s Canons catch-all ERR code basically telling you that something went wrong and it didn’t fall under the other ERR codes. It seems to be mostly lens-body interface issues but not always. Also, I have noticed that with my old XT I would occasionally see it with the larger lenses if the battery was getting low. But try cleaning the contacts, charge up the battery, make sure that the lens is seating all the way and see if it gets better. I know that with some non Canon lenses, especially some older ones, that they may have to be re-chipped on some newer bodies.

The problem with your older lens will be the electronic aperture. Stick it on the camera, extend to 300mm set the aperture to wide open and it might work. My old Sigma does that on mine.