Server mapped drive not accessible error

Set up - Simple work domain with SBS 2003 file server running Active directory. XP Pro client fully updated.

XP client has a mapped drive for 1 of the server drives that has several folders with company information. Also running a database application that has a different mapped drive for access to the database.
After 8 hours or so XP client starts getting drive not accessible error messages. This is highly variable timing but the more times the server is accessed generally makes the time shorter but hardly ever before 7 hours have elapsed from either cold boot or log-in.

Researched this earlier this year and (am kicking myself in the a$$) thought I had found a solution but forgot to either print out or bookmark the answer.
I believe there was a limit to the number of connections in the solution that a reg hack changed but I cannot find the blamed thing again.

Anyone have any ideas on this?
I have no problems accessing the mapped drive until this "timeout" occurs and 3 other comps (2 XP Pro and 1 Win 7) in the domain do not have this problem.