Disabling GreenAddress 2FA ∵ Google Authenticator doesn't generate the correct OTPs for it
The only reason I can think of that would result in the above with a valid OTP seed is invalid OTP settings (but default should work for Google Auth) OR incorrect time on the device OR invalid time (drifted) on the GreenAddress service clock.

I checked for the last one personally and the services clock is fine: in my experience most of the time is time/synchronization on the device.

There is no way of disabling GreenAddress 2FA without 2FA however users that created 2of3 subaccounts can use their two keys to spend/recover and users that enabled email notification with nlocktime can bypass the 2FA after a period of time (by default 90 days, min 1 day, or maximum nlocktime allows)

Thanks