Starting with Data Protector 9.06 in copy\restore sessions, session managers (csm\rsm) use new procedure to select replacement source device if the original is used in another session. It should pick any free device from same library with "Device may be used as source device for object copy" \ "Device may be used for restore" policy enabled and same device tag as original, but it's failing.
Even if there are plenty of free devices matching this criteria session will remain in:
[Warning] From: CSM@hostname "Copy" Time: 06.05.2016 13:30:01
[64:18] Some of the devices are occupied. Session is waiting
for all the devices to get free.
Workaround is to manually change source devices, change request QCCR2A68250 is raised to resolve this problem.