It is obviously preferable, and conducive to more reliable restores, for all applications to be closed at the backup time, but there are many cases where this is not possible, thus Microsoft has created the Volume Shadow Copy Service (VSS) to backup open files on the local machine in a crash resistant state, i.e. files that are open and in use by applications at the backup time. So, our software utilizes VSS by default, though it can be turned off in GUI or via the INI file using the vss option as described below.
On some machines you will encounter VSS errors or warnings during backup such as “Warning, VSS [StartSnapshotSet returned VSS_E_BAD_STATE].” These VSS problems sometimes result from (a) multiple different backup solutions, (b) something wrong with the configuration of VSS on the local computer, and (c) other reasons. Microsoft has several KB (Knowledge Base) articles that describe the cause of VSS issues and offer fixes and solutions.
If you do not need to backup open files then you can turn off our software’s usage of VSS by setting vss to zero in the INI file or by launching the GUI in expert mode and choosing the following on the Expert Settings tab: