[Deezulbub]

I updated to 6.5 yesterday & had a problem setting up my Gmail as well. Even though all my settings were correct, every time my phone would attempt to reach the mail server(s), I would get the same notification to check my username & password.

I was about to contact HTC tech support to see if the 6.5 update was having problems handling Gmail, but, just as I was about to dial, decided to try one more time. For some reason, it worked! I don't know how or why, but I'm now receiving my Gmail on my phone just as I was before the update.

I realize this isn't presenting a solution to your problem. Wish I had a definitive answer for you. I honestly don't know why it wouldn't work for me yesterday, but did today. Several searches turned up a lot of results from users having problems setting up Gmail after the update, but none were about this specific problem. I'll keep looking & post if I find a solution.

Good luck.