I am getting an "unexpected error opening catalog" in my LR5 catalog. Please help! I have windows 7. It seems to only be one of my catalogs with the issue. I have re installed lightroom and installed updates as well.
I had the same issue - after installing Lightroom 5.6 (64 bit version, Windows 8.1) worked for a couple weeks, then I got the unexpected error message this morning. I was going to install a previous version, like 5.5, but it appears Adobe released 5.7 last week so I downloaded the new one and I'm up and running here now!
You can also try navigating to your Lightroom system files folder and removing/deleting the 'Lightroom 5 Catalog.lrcat.lock' and 'Lightroom 5 Catalog.lrcat-journal' files and see if that helps - I've noticed some users have had luck with that method.