There is one other VM whose name ends in a period '.' and that one is backed up without a problem both fully and incrementally:
"VMVCB::\\uranus\VCGuestVm\(DC)ha-datacenter(DC)\vm\TEST Windows 7 Prof."
The configuration is however not quite identical. This one is backed up directly to tape. The failing one goes to a disk deduplication volume first before being copied to tape, and it's only the second step that fails.
Meanwhile, tonight I had another completely different D2D2T job also fail in the copy to tape step after the backup to disk failed. No idea if that's related. This one backs up an Exchange 2010 server, and the error was:
Final error: 0xe00002f7 - Cannot extract mailbox messages from the Exchange backup. Review the job log for more information
V-79-57344-759 - Unable to complete the operation for the following reason: VFF Open Failure. This can be caused by low memory or disk resources.
I found TECH205240 but this isn't a DAG, I did back up to disk, and it's strange that the error shows up on the copy to tape job after the backup job proper completed without errors. Again, no errors in the event log except for a probably unrelated MSExchangeTransport/1035 "LogonDenied error during incoming authentication".