Queue locking issue

XI is been used to migrate data from legacy system to SAP system. Sometimes the queue is getting locked. Once the queue is unlocked manually then the message is processed correctly. Could anyone through some light on the reason for this locking of queues? How can this be avoided? If the locking of the queues cannot be avoided is there any way to unlock the queues? There is a standard report RSQIWKEX available that can be scheduled in SAP system to automatically unlock the queues. I have set the IS configuration parameter

MONITOR QRFC_RESTART_ALLOWED to value 1.I tried executing this report after applying these settings but was not successful in unlocking the queues.

It would be really helpful if anyone can give us a direction in solving this problem.