Agentless Backup of Windows 2003 guest VM's fails with the error
could not take snapshot of the Virtual Machine. ESX Server/vCenter Server reported the following error: An error occured while quiescing the virtual machine.See the virtual machine's event log for details.
UDP 5.0 Update 4
esxi 5.0.0 623860
Guest VM OS: Windows 2003 SP2 x86
Check Windows Event logs inside guest OS and check for VSS errors /writers errors or VMware Tools errors at the time when snapshot failure occurred.
Install VSS roll up update for Windows 2003 in the guest VM if it is not installed already, https://support.microsoft.com/en-us/kb/940349.
Reboot the VM.
Try to take a manual snapshot of the VM from vSphere Client by selecting the below option, if the snapshot is successful then try an Agentless Backup.
(Uncheck the option Snapshot the virtual machine's memory and check the option Quiesce guest file system.)
If the manual snapshot fails, then modify the plan and change the Snapshot Quiescing Method to Microsoft VSS instead of VMware tools and try an agentless backup.
If this also fails, then protect the node using an agent based plan.