Camera Acting Odd w/ Particular Lens
 

I recently purchased a Tamron 24-70 2.8 off eBay last week for $380. I got it for that price because it was a store return and the description stated that it had "focusing issues." I assumed the auto focus didnt work, which is fine with me because I don't use auto focus.

Well I get the lens in and it's been acting odd.

First, the camera wouldn't turn on with that lens attached. Once I played with it a bit, it would finally turn on. Then I kept getting Err 01 when trying to take a photo in manual mode. It works fine in video mode, but manual mode gives me that error.

I read online about cleaning the connections, so I did that with a pencil eraser and it didn't do much. It's very inconsistent turning on and I wouldn't be something I could trust in the field currently. Anyone have this issue before or know how to fix it?