This should be reported over in the Report an Issue section as a possible bug.
And you should take a recent back up copy of this file and check it for damage with Recover or, if you have a copy, FMDiff.
Thank you Phil. I tried checking it for damage and it came out with no issues, it just rebuilt the indexes. Didn't make a difference as the issue is still persisting this morning.
It's weird because I had them keep trying to connect and it took a few minutes of clicking, waiting for it to time out and give the error, and then repeating before it finally prompted for login and let them in. So it seems to be random.