This doesn't apply to IanG, since he specified his library is not shared to other computers. However, I know some MC users are doing this. I thought I'd point out that in Windows XP and Windows 2000 Microsoft enabled a new feature called Opportunistic Locking. This feature is not compatible with any multi-user database software! It will cause corruption of the database if it is not disabled.
There is a registry edit that needs to be done to disable it. If you run MC in a network environment, I suggest you go to Microsoft's Knowledge Base website and search on OPLOCKS. You'll find the article that shows the registry edits to disable oplocks.
I work for a software company that produces a large multi-user database used by govt. and large private sector companies. This OPLOCKS issue has our tech support staff working overtime. Of course the calls always go, "all of a sudden we get db corruption errors several times a day, what's wrong with your program?". This is of course a customer that's been running our software fine since 1998 and all of a sudden it's our problem
. Turns out they installed new XP workstations and the trouble started then. Disable oplocks on all workstations and server and no more corruption errors. Since MC is technically a database, it would be affected similarly if more than 1 person could access the database over a network.