I have only had Ubuntu 14.04 installed for a couple weeks. A couple days ago, whenever I would return from suspend, the password would not be accepted. However, if I restarted my computer, typing the exact same password would work just fine. Any possible way to figure out what is causing this issue?
My comment also works as a partial answer.
After you come back from suspend do the following:
[Ctrl]+[Alt]+F6to leave the X session. You don't have to type anything in to the terminal that appears.
[Ctrl]+[Alt]+F7to come back to the X session. Now you can input the password and it validates properly.
It's not a fix, but a lot easier than rebooting.
For me, only switching to the text console and then back to the graphical one has not been sufficient. On top of this, I had to log in at the text console and shutdown the
fingerprint-helper process from there. After switching back to the X-server console, I was able to continue using my session.
For details, please see my answer on Fingerprint GUI breaks lock screen after suspend.