The false positive thing is happening all over the GM community right now, currently at least A-Squared, AVG, Ikarus and VBA32 report GG2 (and probably a lot of other GM8 games) as infected. Kaspersky initially had the same problem but we already contacted them and they fixed it within a day. Unfortunately I can't find a way to send a report to AVG without being a customer, so could someone (or everyone) of you with AVG do it?
Edit: Kaspersky only fixed the problem for GM8, the old GM7 Gang Garrison is still reported as infected. Since we're switching to GM8 anyway I'd say it's not a big problem, but if it annoys you just contact them yourself.