A CHECKIN LIBVOLUME command is in progress, and the specified volume is needed. However, there is a volume awaiting to be removed from the entry/exit port before the specified volume is inserted into the port of the given library.
The server waits until a REPLY command is issued.
Remove the volume from the library and insert the correct volume into the entry/exit port. Issue a REPLY command, along with the request ID, to tell the server that the volume has been removed and a new volume has been inserted.