I had three Sigma lenses when I bought my 20 D and was told that my 28 to 105 F2.8-4 was compatable. Well it was not and neither was my 105 F 2.8 Macro or my 70 to 300 zoom. So on Wed I sent it to Sigma and today I received them back.
They fixed my 28 to 105 and my Macro but the zoom is a dicontinued model so not parts to fix it with.
Both lenses work fine with the 20 D now.
Just thought you would like to know. A one day turn around at no cost to me, except shipping one way.

$50 to repair what appears to be a broken AF gear, in addition to a free incompatibility upgrade. 
