On a T5 Super Cluster (running 18.104.22.168) I was creating a cascaded standby from an already functional standby using RMAN DUPLICATE and it errored out with
ORA-01671: control file is a backup, cannot make a standby control file
A quick search reveals that it is bug 11715084 that affects most of the 11.x versions except 22.214.171.124. There is a one off patch available for most of the versions or one can install the bundle patch that includes the fix for this patch. I applied BP26 and it worked fine after that.
A rather not so great post about an ORA-00600 error i faced on a standby database. Environement was 126.96.36.199 on Sun Super Cluster machine. MRP process was hitting ORA-00600 while trying to apply a specific archive log.
The error message was something like this
MRP0: Background Media Recovery terminated with error 600
Errors in file /u01/app/oracle/product/188.8.131.52/diag/diag/rdbms/xxxprd/xxxprd1/trace/xxxprd1_pr00_6342.trc:
ORA-00600: internal error code, arguments: , , , , , , , , , , , 
Some googling and MOS searches revealed that the error was due to corrupted archive log file. Recopying the archive file from primary and restarting the recovery resolved the issue. The fist argument of the ORA-600 is actually the sequence no of the archive it is trying to apply.