Problem:
NetBackup SAN Client backup of Microsoft SQL Server fails with status code 6
15:21:38.819 [8108.7324] <16> AttachShMForBackup: Unable to open shared memory (Global\NetBackup Media Manager SHM Path 84222078 2900): OS error 5
15:21:38.819 [8108.7324] <16> SetupShMforBackup: Returned with error 12 from AttachShMForBackup
15:21:38.819 [8108.7324] <16> handshake: ERR - failed setting up for shared mem
Error 5 is ACCESS_DENIED
Since the shared memory is created by the NetBackup San Client Service and written to by the database agent, the database agent must have permission to access the shared memory.
Resolution:
The database agent runs under the NetBackup Client service. This service must be started with an account that will have privileges to access shared memory created by the account that the NetBackup SAN Client service runs under. This can be controlled via the services section of the Computer management interface.
Simply right click on "My Computer", then select manage. In the Computer Management interface. select "Services and Applications" then Services. In the Right panel find the "NetBackup Client Service". right click and select properties. In properties select the "Log On" tab. In this tab the account used by this service can be designated. Be sure that the designated account has the privileges needed in order to access shared memory created by the account the NetBackup San Client service logs on as.
Mentions SQL instead of Oracle though it looks like the same trouble!
http://www.symantec.com/business/support/index?page=content&id=TECH74570