rman: cannot delete device type

[krempe]

Hi,

I configured a defalut device type "sbt_tape" with RMAN, "show all" says:

CONFIGURE CHANNEL DEVICE TYPE 'SBT_TAPE' PARMS '???nsr_env=(nsr_server=su10, nsr_group=default)';

Maybe the "???" is the problem, but I cannnot delete the device:
RMAN> CONFIGURE CHANNEL DEVICE TYPE 'SBT_TAPE' CLEAR;

old RMAN configuration parameters:
CONFIGURE CHANNEL DEVICE TYPE 'SBT_TAPE' PARMS '???nsr_env=(nsr_server=su10, nsr_group=default)';
old RMAN configuration parameters are successfully deleted

but "show all" says:
CONFIGURE CHANNEL DEVICE TYPE 'SBT_TAPE' PARMS '???nsr_env=(nsr_server=su10, nsr_group=default)';

Reconfigure of DEVICE TYPE 'SBT_TAPE' works, but than "show all" says:
RMAN-12010: automatic channel allocation initialization failed
RMAN-12014: multiple records for default channel configuration for SBT_TAPE found in catalog

Any ideas?

Thanks,