Disabling VSS can cause more issues, as DFS backups rely hugely on VSS , as VSS will tape a snapshot of the DFS data even if its been use by users or if the DFS data is getting replicated along the sites.
Right now fixing the VSS should be the 1st priority as disabling it wont solve the purpose.
I Would suggest you to check the space on the S : volumme, also try to set the volume`s storage are size to no limit, by right clicking on the volume and navigating to the Shadow Copies Tab\Settings button and the no limit check for in front of the Maximum size.