fight it and get a blizzard authenticator if you don't already have one, i love mine.

I've never used the guild bank for money transfers between my team.
I could see how it might be fast and convenient but bliz may have had to implement special safe guards (some type of auto bans) for people who steal accounts and raid a guild vaults. :cursing:
I have a bank toon that does all of my selling but when I need something on another toon I usually mail it or go meet the bank toon and transfer it that way.
I rarely work hard to make gold though, only when i'm in need like buying mounts do I bother working the AH very hard.