That error means that one or more of the VSS writers required for backup are failing for some reason.

Writers almost always fail for a reason. Normally this has little to do with the backup application itself, although it can happen if the application is feeding the writers data it doesn't understand. That's pretty rare though.

If things are broken after an upgrade, I recommend you uninstall ZCB. During uninstallation you will be asked if you want to preserve configuration. Say yes. Then reinstall.

If the issues continue after that, please enable DEBUG logging, reproduce the error, and send logs as shown