I’ve been struggling with my online backup AltDrive recently. It seemed to continue a backup started a couple of days ago but never getting past the phase of Creating Shadow Copy. When I cancelled the backup process, I was able to start over but still the previous backup continued to hang in the progress window. I tried all sorts of things related to shadow copy but with no avail. I uninstalled the client (keeping settings because I didn’t want to lose backed up data) and installed a fresh version, no change.
What finally helped was to delete content of C:\Windows\System32\config\systemprofile\AppData\Local\AltdriveWBHomeService\tmp. I suppose the hanging backup was interrupted when I shut the computer down a few days ago, and some files were left in an inconsistent state.
Edit: New location is C:\ProgramData\AltdriveWBHomeService\tmp