If you are using Adobe Lightroom 5 and have recently upgraded to Windows 10 (as 25 million people did), you may have seen this dreaded message while opening Lightroom, saying it can't open its catalog due to "unexpected error".

Lightroom error dialog

Don't worry about your catalogs, your data is safe, issue appeared because apparently, Windows 10 changed access permissions of system-managed folders, such as Pictures and My Documents.

To fix this issue, you have two solutions:

  1. you can run Lightroom as administrator (right-click LR icon, click on "Run as Administrator"),
  2. or you can move your catalog files from system-managed folder to some other location on your disk.

First solution temporarily elevates Lightrooms permission to administrator level, so it can access and modify it's files even in system-managed folders, meaning you'll need to run Lightroom as administrator each and every time; second solution is permanent - catalog files are moved to different location which does not need elevated access rights. That's the reason people having their catalog in non-system locations never saw the message, in the first place.

I don't own Lightroom 6, I don't know if this issue is present in newer version, but according to quick googling, all versions older than 6 have the same problem. Also, this affects only Windows version of Lightroom, and apparently, only Windows 10 users.

If you plan to upgrade Windows, please, backup your catalogs. Also, backup your catalogs regardless of your plans of upgrading, OS, or LR version you're using.