The error may be reported during Daily or Weekly admin activities.
DS-Client uses SQL Express instance for its internal databases. These editions have a 2 GB (MSE2000), 4 GB (SQL Express 2005/2008) or 10 GB (SQL Express 2008R2 and higher) database size limitation.
When any of DS-Client databases reaches the size defined in DS-User > Setup > Configuration > Advanced > Miscellaneous >DBHighWaterMark, DS-Client will try to automatically create an additional database and move there the info corresponding to an existing backup set located in the existing database that approached the size limit so that the space condition is resolved. If the info corresponding to any backup set is too large to be moved, this error is reported.
Upgrade to a SQL full version, which does not have a size limitation imposed.