The VeeamVssSupport service cannot be installed because it was never uninstalled. It was marked for deletion instead of being deleted. It cannot be removed, but will be removed automatically when the guest OS reboots.
Typically this is due to one of the following programs being open at the time the deletion command was received:
- mmc.exe (Services.msc is the most common example, but any MMC console may cause this error)
- Task Manager
- Sysinternals Process Explorer