RMAN-06026: some targets not found - aborting restore

Hi,

I am getting this error while giving a command after the rman backup.

restore validate database;


Error
datafile 23 will be created automatically during restore operation
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of restore command at 11/26/2012 22:23:32
RMAN-06026: some targets not found - aborting restore


Awaiting for your reply.

Regards,
Amit