Problem to configure RMAN 11gR2 with EMC Data Domain

Hello together,
have anywhere an idea why oracle and the data domain mm-library runs not correct.

The error is:
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03009: failure of allocate command on C1 channel at 06/17/2013 12:37:09
ORA-19554: error allocating device, device type: SBT_TAPE, device name:
ORA-27211: Failed to load Media Management Library
Additional information: 3970

Many different syntax in the configuration create the same error.

CONFIGURE CHANNEL DEVICE TYPE 'SBT_TAPE' PARMS 'BLKSIZE=1048576,
SBT_LIBRARY=/opt/apps/oracle/product/11.2.0/lib/libddobk.so,
ENV=(STORAGE_UNIT=su_ito_rman_dir,BACKUP_HOST=hostname....,ORACLE_HOME=/opt/apps/oracle/product/11.2.0)';

RUN {
ALLOCATE CHANNEL C1 TYPE 'SBT_TAPE' PARMS