backup fails when backing up system reserved partition

Specs:
server 2008r2 fully patched
acronis latest.

issue:
Just had to do a scratch reload of the server. installed acronis and imported job. job fails when backing up full disk (all partitions)

created new job and new backup location on NAS. same issue.

I get the error: The shadow copy provider had an unexpected error while trying to process the specified operation' I ran through all the steps to fix vss errors as described: https://kb.acronis.com/content/37472
doesnt help and vss is working fine everywhere else.

I decided to narrow it down a bit. I can back up the C and D partitions together or separately just fine. the problem occurs when I try to back up the system reserved partition.

Any ideas?