Not sure I understand exactly what you're doing (I am mystified by "q scr 
cancel"?), but maybe this can help.  A common workaround is to have the script 
check a return code, then define (or change the start time of) an admin 
schedule that invokes a script, which can check a return code, define an admin 
schedule that invokes a script, etc.    

For instance here is how I prevent a reclaim stgpool from running if the backup 
for a particular client (which backs up direct to tape in that pool) is still 
running.  If the script finds a backup in progress, it reschedules for 2 hours 
later, otherwise it runs immediately:  

tsm: LOCAL_SERVER1>q script ELPROBLEMO_reclaim_offsite f=raw
/* This script checks to see if ELPROBLEMO is currently backing up before 
starting reclamation on the  */
/* ELPROBLEMO_OFFSITE stgpool                                                   
                       */
/* If ELPROBLEMO is not currently backing up, it starts 
ELPROBLEMO_reclaim_offite                   */
/* If ELPROBLEMO is currently backing up, this script reschedules itself in 2 
hours               */
/* see if ELPROBLEMO is currently backing up */
select * from sessions where client_name='ELPROBLEMO'  /* and is holding a 
tape? */
if (RC_OK) goto reschedule
/* ELPROBLEMO not running, so start the reclamation */
reclaim stgpool  ELPROBLEMO_offsite_pool threshold=65 duration=480 wait=yes
exit
RESCHEDULE:
update schedule resched_ELPROBLEMO_recl_offsite type=admin starttime=now+2 
expiration=today
exit

And here is the definition of the resched schedule that got updated:

tsm: LOCAL_SERVER1>q schedule resched_ELPROBLEMO_recl_offsite type=admin f=d

                 Schedule Name: RESCHED_ELPROBLEMO_RECL_OFFSITE
                   Description:
                       Command: reclaim stgpool ELPROBLEMO_OFFSITE_POOL 
THRESHOLD=65 DUR=480 wait=yes
                      Priority: 5
               Start Date/Time: 02/18/2011 11:57:56
                      Duration: 10 Minute(s)
                Schedule Style: Classic
                        Period: One Time
                   Day of Week: Any
                         Month:

And you could easily change the RESCHED_ELPROBLEMO_RECL_OFFSITE to invoke 
another script that checks again to see if the backup is STILL running, and do 
the reschedule again, etc.

W