Yes, I've seen this error too:
Error Code: [19:1047] Description: Checking if the index is in cache.
It's an Oracle RMAN backup (Selective Online Full) on a Solaris 10 server (it's in a zone) with the media agent being the Solaris global zone. (IE nothing to do with AV)
Strangely, the job appears to still be running though, so I'm not sure if it's caused a problem with the backup. I can't find any reference to it in the jobs log files. I wish these errors were better documented!