When attempting tasks on a geodatabase containing versioned data (ex: compress, reconcile/post, or synchronizing a replica), the following error is encountered:
Error: Underlying DBMS error Subquery returned more than 1 value. This is not permitted when the subquery follows=,!=,<= or when the subquery is used as expression.
This error occurs when custom triggers are created on versioned feature classes and multiple records are being added to version tables (such as the delta tables) without going through the proper workflow. This results in an incorrect record count during geodatabase tasks such as compress, reconcile/post, or synchronization.
Custom triggers to perform automatic updates are not supported in ArcGIS. To update versioned data using SQL, use the versioned view of each respective feature class (see the Related Information section below).
To resolve this issue, disable or drop any custom triggers and attempt the geodatabase maintenance process again.
If the error is experienced when synchronizing a replica, unregister the existing replica, re-create the replica, and perform edits in the recommended workflow before re-synchronizing the replicas.
If the error is experienced during the reconcile or post of an edited version, delete the problematic version and redo any edits done in that version. For more information, refer to the following web help page, ArcMap: The version editing process.