>Starting from a certain hour in the early evening (some 18u, others a bit later) they start getting Error reading file-errors.

This could be related to problems in renewing DHCP IP address on you workstation.

I had a similar problem recently that at the 12 hour mark--after I rebooted my machine--the DHCP server failed to renew the ip address. As a result, the network connection would disconnect and give error reading file in VFP.

Check the event viewer on the XP, 2000, and NT machines to see if there are errors.

--Paul