A lot of times you must have encountered the error mentioned below
SBL-DAT-00523 : The selected record has been modified by another user since it was retrieved.
This error message signifies that somebody else was quicker than you and has already modified the record, so you need to perform the update again. This is common occurring scenario where lot of updates are happening either thorough Policy Workflows or Asynchronous requests in addition to synchronous updates either on UI or scripting. This article attempts to explain How Siebel Applications handle the concurrent attempts to update a record?.