The error is reported during backups for sets using VSS.
Another VSS-based backup solution interrupts the DS-Client backup.
If two VSS-based backup solutions must protect the same application files / volume ensure the backups do not overlap. The DS-Client uses the Microsoft VSS provider, if a hardware VSS provider is installed on the backup source server it will usually become the default one and the backups with DS-Client cannot be performed.
To list the VSS providers on the backup target computer, run from an elevated command prompt window the command: vssadmin list providers