ANR9779E

Explanation
 The library manager was unable to assign a drive
to the library client. There are a couple of situations that can cause
this error.
 All drives are currently allocated to other library clients or
the library manager.
The request for a specific drive cannot be satisfied.  This can
occur if a drive on the library client side is marked offline or is
currently busy with another process.
A communication error occurred during the request to mount a volume.
The requested volume was not present in the library manager's
inventory

System action
 None.

User response
 Verify that a drive is available on the library
manager side and the drive is currently not busy or marked offline
on the library client.  Set the mount retention on the device class
on the library manager and the library clients to a lower value. 
Using a lower mount retention value can free up drives.