recover copy of database failed with ORA-15012

Problem description:

During the incrementally Updated Backup, I got following error message 
while executing command -- "recover copy of database with tag '$TAGAME';" 

recovering datafile copy file number=00016 name=+RAC_FLASH/RACprd/datafile/index_medium.1854.813296975
channel oem_disk_backup: reading from backup piece +RAC_FLASH/RACprd/backupset/2013_05_25/nnndn1_RACprd_lvl0_0.2907.816333595
released channel: oem_disk_backup
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of recover command at 05/25/2013 21:40:57
ORA-19870: error while restoring backup piece +RAC_FLASH/RACprd/backupset/2013_05_25/nnndn1_RACprd_lvl0_0.2907.816333595
ORA-19625: error identifying file +RAC_FLASH/RACprd/datafile/index_medium.1854.813296975
ORA-17503: ksfdopn:2 Failed to open file +RAC_FLASH/RACprd/datafile/index_medium.1854.813296975
ORA-15012: ASM file '+RAC_FLASH/RACprd/datafile/index_medium.1854.813296975' does not exist

Cause:
The copy of the data files are marked to be Available in the RMAN repository. 
So during an incremental merge, RMAN expects to merge the incremental 1 backup to the datafile copies.

Solution:
RMAN> crosscheck copy of database;