This evening I was getting a 400 Error Bad Request after logging into Gmail. I’m not sure what was up, but I cleared my browser cache and cookies and still nothing.

I use Google Chrome as a browser, so I fired off an Incognito session and was able to log in absolutely fine. Strange! This told be it was something up in the main version of Chrome; but what?

I did a Google search for “Gmail 400 bad request” and the first item that was return suggested the following:

This I did an there was no change. Next it told me to:

There where also the following options, if needed:

Now, I’m not saying any of these will fix your issue, but they are worth trying.