We just replaced 2 clustered servers that were running W2K and SQL 2000 with 2 new clustered servers running Win 2003 and SQL 2000. Since these servers were replaced, all of our previous scheduled jobs to backup to a disk location on one of the clustered servers started failing.

BackupDiskFile::RequestDurableMedia: failure on backup device '\\sqlXXXX\backups\SysBkups\XXX\20080707_010603_XXXX_XXXX_Db.bak'. Operating system error 64(The specified network name is no longer available.).

We worked with MS to resolve. And the tech said that it was caused by the SQL server sending the packets not receiving the responses in time so it was perceived that there was a problem with the network. What resolved our problem was to add a SessTimeout setting with the DWORD value as 360 to the Win 2003 or Win2K registry on the SQL servers that the backups are failing. By adding this setting the server waits longer for the response. See this article for info on how to add.

https://www.microsoft.com/technet/prodtechnol/windows2000serv/reskit/regentry/58909.mspx?mfr=true

Hope this helps