Only user processes can be killed
Msg 6107, Level 14, State 1, Line 1
Only user processes can be killed.
This error message appears when you try to terminate a system process via the KILL command.
The T-SQL statement can be parsed, but causes the error at runtime.
Error of the Severity Level 14 are generated by the user and can be fixed by the SQL Server user. System processes cannot be terminated via KILL
All versions of SQL Server
In the above example we try to terminate the process-ID 1 via KILL. Because this ID is reserved for system processes, the error is raised.