If it is to do with the upgrade, then it has to be related to one of the features available in paid & not in free, I'd imagine the main suspects would be CBT & Image Guardian, & probably something additional unique to setups that have an issue, identifying that unique thing is probably key, since most people don't have a problem.
Any bug in such a case could be in Macruium, or equally as likely in that other yet to be identified thing.

Macrium can't even work around whatever it is without knowing what it is though, & there may come a moment when you have to contact support directly.

I contacted support for the original issue - Invalid (The user name or password is incorrect.) - they even remoted into my desktop but couldn't figure out the issue.
I ended up suggestion we try creating a new user on the NAS which APPEARED to work but it didn't - one subsequent backup ran correctly but then it started giving me the same error.

The issue is so convoluted at this point that I just don't know who to point the finger at - Macrium or Windows, or in the previous case, Synology.

Just for kicks, I'll try reinstalling the free version after work and see what happens with that.

Update:

Local backups have been running ok for the past few days since running the Dism commands. And while I would have agreed that it probably wouldn't do anything, somehow it has.

Of course I'll give it a few more days to see if it's really sticking.

Still would love to get backups working straight to the NAS again but I don't think I can troubleshoot anymore!

Reviving this thread since I am still receiving the VSS error below. It happens randomly. Backups may run fine for a few days and then this error will pop up.
There's no other backup software, windows updates are scheduled way later in the day and I can't think of anything else that would be using VSS.

I've tried the VSS fix but that doesn't seem to do much.
I've run the 'vssadmin list writers' command - usually everything is in a stable state but then there will be a few that are 'waiting for completion' (from what I've read, that's pretty normal but not sure why they wouldn't be stable)

Looking for any other suggestions.

Thank you!

Failed: Failed - 0x80042316 - IDispatch error #8470 - Retrying without VSS Writers

ERROR: COM call "m_pVssObject->StartSnapshotSet(&m_latestSnapshotSetID)" failed.
- Returned HRESULT = 0x80042316
- Error text: VSS_E_SNAPSHOT_SET_IN_PROGRESS
ERROR: COM call "m_pVssObject->BackupComplete(&pAsync)" failed.
- Returned HRESULT = 0x80042301
- Error text: VSS_E_BAD_STATE
ERROR: COM call "m_pVssObject->StartSnapshotSet(&m_latestSnapshotSetID)" failed.
- Returned HRESULT = 0x80042316
- Error text: VSS_E_SNAPSHOT_SET_IN_PROGRESS

Backup aborted! - Failed To Create Volume Snapshot. Failed - 0x80042316 - IDispatch error #8470