all the server error messages and lock ups i have received today are becoming increasingly frustrating...
I once had it tell me my account no longer existed. I had a nervous hour or so when that happened. That was on the browser.
Once on the mobile app, it told me my password was not my password. I could still play on the browser that time, so I wasn't quite as bad as 'ack! whatdoyoumeanIdon'thaveacity?!' - but I wasn't too happy about that either. It eventually worked itself out. (I use an emulator program to access the app on my laptop, so there's no cache to clear afaik. Now someone will tell me I'm wrong and explain how to do it.
)
The advice that support gave me whenever I had a problem with the server was to clear cache and cookies, then close my browser (all open tabs and windows). When you reopen your browser after doing that, you're essentially 'rebooting' the program. If that doesn't solve the problem, sometimes rebooting the computer helps. This is especially true if you have any kind of computer updates, especially OS updates, pending.
If you're on the app, my only advice is to file a bug report. Sorry I can't be more helpful there.