APAR OA35253 discusses an interesting scenario when using KILL versus KILL FORCE. While OMEGAMON does not require that a user issue a KILL before doing a KILL FORCE, there is apparently an occasional timing issue where if you try doing a KILL without first doing the KILL FORCE, the command may not work, and generate an error message.
Now you may see the following if a KILL FORCE is attempted without a prior KILL. The tool will process the command as a KILL, and a message will be displayed:
OC0550: FORCE OPTION REMOVED - MUST TRY KILL FIRST