Lens compatibility with firmware upgrade

I bought a 7D with an old firmware. It has a Tamron 2.8 VC lens. Worked well till i updated the firmware. Now whenever i take a shot, it shows error that body is not communicating with lens and that i should clean contacts. (I did clean it anyways) I wish to revert to that old firmware, and not able to do so. I can move forward and not backward.. (With exception of 2.0.5 to 2.0.3)

On that note, can anyone help and guide if there is any way to force downgrade to 1.2.5? Please help..