I've been trying to log into my Gmail accounts on Thunderbird on my Windows machine, and each time I get that error message in the title. Google recognizes the account as signed into Thunderbird, and I had to go into the Google Account and sign out from an instance of each of my attempts. I made sure cookies are allowed, and using oauth2. Not sure what to do here? Is anyone having the same issue? Update: I just downloaded spark and logged in no problem. Also, the Thunderbird on my mac is logged in just fine.