rman backup cloud moduel for s3 error

error message:
RMAN> BACKUP DEVICE TYPE SBT  AS COMPRESSED BACKUPSET CURRENT CONTROLFILE;
Starting backup at 27-JUL-12
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of backup command at 07/27/2012 11:37:48
ORA-19554: error allocating device, device type: SBT_TAPE, device name:
ORA-27023: skgfqsbi: media manager protocol error
ORA-19511: Error received from media manager layer, error text:
   KBHS-00715: HTTP error occurred 'client-error'
KBHS-00703: unable to connect to HTTP server oracle-sbt-license.s3.amazonaws.com; received ORA-12535
LFI-00108: Open expect the file [ewallet][p12] to exist.

This error was cleared by itself after 3 hours.

I cannot find out the cause.

to find out cloud moduel parameter

strings $ORACLE_HOME/lib/libosbws12.so | grep '^OSB_' | sort

strings $ORACLE_HOME/lib/libosbws12.so | grep '^_OSB_' | sort

reference:
http://www.idevelopment.info/data/AWS/AWS_Tips/Oracle_on_AWS/ORAAWS_15.shtml