mystery RMAN-06091 error

 Hi everyone,

We have a RMAN script to clean the obsolete backup files on the disk.

However somehow this script seems to have some kind of temper. It worked one day, but not worked on another day.

When it doesn't work, it always give us RMAN-06091 error even I have "allocate channel" command at the beginning.

I am thinking this could be caused from OS level, but I do not know where to start looking.

Please advice.

Thanks,

------------------ RMAN script we use -------------------

host 'date';
allocate channel for maintenance type disk ;
 
host 'date';
crosscheck backup completed before 'sysdate-21';