After spending a couple of hours of doing research, I finally figured out why my email has been working off and on for the last few weeks. I have a Droid Bionic and I use the standard Mortorola email widget. It stopped working completely this morning so I was finally fed up with it. I was getting the error along the lines of "invalid credentials, please check settings or try again"
I tried deleting the account, but then I couldn't re-create it because it said the password was invalid. I tried installing K9 mail, and it couldn't connect either. However, the Gmail app was working fine. It was blowing my mind.
then i found this article:
then i found this link:
After clicking on this stupid link, already signed into Gmail, my email on my phone came back! I don't know why this screen wasn't showing up when i was signing into gmail from my computer, but this link did the trick.