350d error 99 on one lens only? lens fault?

Only happens to me on one lens... all my others are fine... thanks...

yes i cleaned the contacts,,,

Which lens? All the time, or just once and a while?

i'm going to take a wild guess and say it's the sigma..

error 99 with one lens usually results when that lens has
a: dirty contacts
b:sticky/broken aperture
c: water damage

tamron 28 75mm I'm guessing broken aperture...

I had a similar problem with a sticky aperture on a Tokina 24-200. Use your DOF button while looking into the lens to see if it seems to be consitantly opening and closing the aperture.