Hey, newbie here.
I have the same problem, I am working using Archicad 13 on windows platform - have no serious problem until last Thursday, I started to get the same dialog box 'this file is in use by ...' & if I choose either open with exclusive access or read-only - mostly it will end up freezing when Archicad trying to load variables then load the bug report.
I've tried to delete the .lck file, it's only prevent the dialog box from appearing, but it will still failed to open.
I've tried to renaming it and save on other location, but still no success.
Any idea what went wrong? I don't have a clue if there is any fault with the object library, since if I manage to open the file - everything seemed to be in place.