Server Crashes when attempting to write to a shared network drive

I have 5 clients mapped to a network share on a newly installed SBS 2K3.
One 
client can read and write to the server, the other 4 can read but when 
writing to the mapped drive, it crashes the server.

Permissions on the Server are Everyone Full Control on both sharing and 
security.

Event logs only say unexpected shut down occurred at  X.X

Full patches/ Updates  applied.

Ltest defs Trend Micro

I am totally stumped .

If anyone has any ideas ????