Hi David,
Could you provide related screenshots of the error?
To upload screenshots, you can click Use rich formatting in the forum and then click the icon of Insert Media.
Besides, it is suggested you try the following steps first:
1. Try the Repair OneDrive for Business option if you can see it.
2. Try re-syncing the library via Preferences > About > Unlink OneDrive for Business.
3. Delete the OfficeFileCache folder (not sure if you mean this by saying “deleting the file cache”).
1) Quit OneDrive for Business.
2) Go to ~/Library/Group Containers/UBF8T346G9.Office/Microsoft/AppData/Microsoft/Office/15.0/ and delete the OfficeFileCache folder.
3) Reboot OneDrive for Business.
Thanks,
Eric Yang