If you tell us what you did that caused the error, it may be easier to help you fix it. It's probably there.

I have same issue today. I did two things: First removed Waterfox using REVO Unstaller. REBOOTED

I might have had RATAIL malware so decided to install Charter Security Suite since was free with my account. Rebooted.

At this point is when I wanted to check my email. Got error. Reall need this fixed as I have years of email that I need. Thanks

ggrussell, your issue may be much different, as I am unaware of how Waterfox or the malware issue. I encourage doing a separate post to improve odds of someone familar to assist.