With windows 2003 server SP1, I've got the same problem.
My windows 2003 standard server (in a vmware gsx server box) shall make a backup (with its backup application) to a windows 2003 sbs premium edition server (on a separate, physical machine).
I only face the problem when the backup application runs; other applications or normal network traffic don't produce such errors.
Both servers are running with latest service packs/updates.
This is the detailed message:
Windows was unable to save all the data for the file
\Device\WinDfs\R:00000000000589f9\srv10.lan.compumaster.de\dfs\AdminBackups\SystemBackups\srv04.lan.compumaster.de\OtherServerData.bkf. The data has been lost. This error may be caused by a failure of
Another event log item is for event source MRxSmb, ID 50:
\{Delayed Write Failed} Windows was unable to save all the data for the file \Device\LanmanRedirector. The data has been lost. This error may be caused by a failure of your computer hardware or network connection. Please try to save this file elsewhere.
For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.