Hi,
If cmclean.sql is run when the concurrent managers are up and running ,the script will not be able to clean and remove the rows from the concurrent manager process and request tables as the ICM and other managers will be holding locks on these tables.
So its better to shutdown the concurrent manager cleanly and then run the cmclean.sql

Regards
Rohit S Nirkhe,Oracle/Apps DBA
OCP 8i,9i