Is this a camera BODY problem or LENS problem?

I own (2) Canon 20D bodies and (1) 1DmkIIn body. I own a Tamron 28-105 2.8 lens that I have used for several years. I think I bought it on here from someone. It has been a great lens. I have never had an issue with it. Recently while getting ready for a wedding I got an "error 99" on a 20D body. I tried all the usual fixes such as shutting off and back on, removing lens then remounting, remove batteries then replace, cleaned the contacts on both the lens and bodies...but nothing seems to work. So I went to my back up 20D body and it too was getting the same "error 99" with this lens mounted. I then switched to my 1DmkIIn body and everything seems to work ok with this same lens mounted.
So I'm very confused as to if I have a lens problem or two body problems. All three camera bodies work just fine with other lenses but my 20D's do not want to work with this Tamron 28-105.
Anyone got any ideas?

So either two 20D bodies quit working with only the Tammy at the same time or the lens has a problem...

I had this same type of issue happen with a CF card and only on one body (40D). The card would work in any other camera and other CF cards would work in the body. I ended up selling the body on eBay for parts after Canon quoted me a repair cost that was $100 less than it cost to replace the body.