Could not lock request

There are four requesting with running phase with normal status (All are same request) since long time when I try to cancel any one of them it says “Could not lock request”.

When I try from back end as below it seems hanging, 20 minute it ran so I canceled. Suggest me how could I cancel them?

Answer-

1. Shutdown the concurrent managers.
2. Connect apps
3. Run the cmclean.sql script 
4. Start your concurrent managers.

Correct, just make sure you commit the changes after you run the script.

Please note that you will get the same error you had before if the CM is up or if there are any locks on the concurrent manager/request tables.

OR.

I would suggest you use cmclean.sql script - this will require some downtime.

Concurrent Processing - CMCLEAN.SQL - Non Destructive Script to Clean Concurrent Manager Tables [ID 134007.1]