Our TSM server is on version 6.3.2.0 and lin_tape is at 1.74.0, and we have the 
same problem. It does not affect all paths, just some. You may see this error 
in the Activity Log when you try to start the affected path: 

02/05/2013 11:54:22      ANR1819E  A DB2 instance ID cannot be used to open 
device 
                          file /dev/IBMtape25n.  (SESSION: 12245)               
   
02/05/2013 11:54:22      ANR8420E DEFINE PATH: An I/O error occurred while      
   
                          accessing drive VDR25. (SESSION: 12245)               
   

There is a Technote about ANR1819E  at 
http://www-01.ibm.com/support/docview.wss?uid=swg21321130 which says the cause 
is a non-root user issuing the DEFINE PATH command. But, here is the 
permissions on the macro we use to define that paths:  -rw-r--r-- 1 root root 
3157 Dec 23 12:50 vdr-path-def.mac

These are virtual drives on a VTL, and I don't think we had had this problem 
before it.  There are no physical drives attached to the same TSM server. 

Keith