Unanswered: Odd tale for your amusement
Not a plea for help, but something that might be useful!
One of my colleagues started receiving error 2501 when trying to open a database. It happened at random, with no logical cause (no system changes or anything). However, I could get into it with no problem.
This particular database was written in Access 2000 in 2003 by a third party, and makes use of Access security (*shudder*). We have a shortcut that incorporates the location of MSACCESS.EXE, the location of the front end and the location of the work group file. The latter two were set up with drive letters at the start of the paths. I have a copy of the shortcut that I had customised, as when I changed roles some years ago, my network privileges changed along with my drive mappings.
After poking various things and playing around with his default printer settings, I decided to try creating a new copy of the shortcut, this time with full UNC paths for the latter two arguments. Would you believe? It worked!
10% of magic is knowing something that no-one else does. The rest is misdirection.