Sounds like two different issues one related to memory pressure and the other one is Hotfix for SQLServerWriter for 2005.
I have not applied these updates since I most likely will use SP3 instructions in KB913648.
SQLVDI Error log
SQLVDI: Loc=CVDS::Cleanup. Desc=Release(ClientAliveMutex). ErrorCode=(288)Attempt to release mutex not owned by caller.
. Process=220. Thread=7092. Client. Instance=. VD=.
A new Volume Shadow Copy Service update is now available that fixes various Volume Shadow Copy Service problems in Windows Server 2003
FIX: Error messages and an event may be logged when you use the Virtual Device Interface in SQL Server 2005 or in SQL Server 2000
The VSS I/O error log stated from Netbackup which I was not using but calls the same SQLServerWriter VSS as the software I was using. Leaving larger amount memory free on that SQL Server seemed to fix that issue.
Event SQL Server VSS log
BackupVirtualDeviceFile::SendFileInfoBegin: failure on backup device . Operating system error 995(The I/O operation has been aborted because of either a thread exit or an application request.).
The SQL Server database backup exits with a Status 6 in Activity Monitor when using the NetBackup SQL Server extension and a status 995 is reported in the SQL Server errorlog.