Error during quiescing, VssSyncStart operation failed: IDispatch error #8451 (0x80042303)

If you see the following error while taking a snapshot for a virtual machine backup, the resolution below may work for you:

Warning message from …: The guest OS has reported an error during quiescing. The error code was: 5 The error message was: VssSyncStart operation failed: IDispatch error #8451 (0x80042303)

First you can try to re-register the VSS components as described in this post:
TSM VM Backup + error during quiescing, error code 5, IDispatch error #8472 (0x80042318)

If you find no other resolution, you can remove the VSS component from the windows guest operating system, provided as part vo the VMware Tools.
In this case older sync drivers will be used – and you have a good chance that this will solve your problem.

How to remove the VSS component:

• right-click the VM and select “Guest” – “Install/Upgrade VMware Tools”
• select “Interactive Tools Upgrade”
• log-on to the virtual machine and start the VMware Tools Setup (you can start it via Explorer – DVD Drive)
• select “Custom”:
  
• deselect the “VSS Support” (Volume Shadow Copy Service Support)
  
• now finish the wizzard – done!

If possible reboot the virtual machine. Backup should work without a reboot, too – but it is recommended…