RMAN-08138: WARNING: archived log not deleted - must create more backups

Backup was successful but We were getting this warning.
RMAN-08138: WARNING: archived log not deleted - must create more backups
archived log file name=/paths/archive/dbprd/2_851_798595897.dbf thread=2 sequence=851


cd /paths/archive/dbprd
ls

1_1024_798595897.dbf
2_884_798595897.dbf
1_1025_798595897.dbf
2_885_798595897.dbf
2_886_798595897.dbf
1_1026_798595897.dbf
1_1027_798595897.dbf
2_887_798595897.dbf

2_851_798595897.dbf is not available in the above list. so i checked in RMAN


RMAN> list archivelog all;

using target database control file instead of recovery catalog
List of Archived Log Copies for database with db_unique_name MCRLPRD
=====================================================================

Key     Thrd Seq     S Low Time
------- ---- ------- - --------------
2125    1    1024    A 08/21/13:19:37         Name: /paths/archive/dbprd/1_1024_798595897.dbf
2127    1    1025    A 08/22/13:03:00         Name: /paths/archive/dbprd/1_1025_798595897.dbf
2130    1    1026    A 08/22/13:17:36         Name: /paths/archive/dbprd/1_1026_798595897.dbf
2131    1    1027    A 08/22/13:19:36         Name: /paths/archive/dbprd/1_1027_798595897.dbf
2062    2    851     X 08/11/13:01:23         Name: /paths/archive/dbprd/2_851_798595897.dbf
2126    2    884     A 08/21/13:19:37         Name: /paths/archive/dbprd/2_884_798595897.dbf
2128    2    885     A 08/22/13:17:36         Name: /paths/archive/dbprd/2_885_798595897.dbf
2129    2    886     A 08/22/13:19:01         Name: /paths/archive/dbprd/2_886_798595897.dbf
2132    2    887     A 08/22/13:19:36         Name: /paths/archive/dbprd/2_887_798595897.dbf



It is listed in RMAN, but it is expired

So i included the below statement in backup script and Warning is no more.

delete noprompt expired archivelog all;