ORA-19606

Oracle 11.2.0.4 Std Ed One 64-bit

Oracle Linux 5

Got this on a backup last night:

RMAN> delete force noprompt obsolete;

RMAN retention policy will be applied to the command

RMAN retention policy is set to recovery window of 6 days

using channel ORA_DISK_1

Deleting the following obsolete backups and copies:

Type                 Key    Completion Time    Filename/Handle

-------------------- ------ ------------------ --------------------

Control File Copy     136185904 06-Jul-2016 09:18:54 /u01/app/oracle/product/11.2.0.4/dbhome_1/dbs/snapcf_cognosprd.f

RMAN-00571: ===========================================================

RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============

RMAN-00571: ===========================================================

RMAN-03009: failure of delete command on ORA_DISK_1 channel at 07/14/2016 00:01:09

ORA-19606: Cannot copy or restore to snapshot control file

Checking MOS notes, then googling around, I found a lot of stuff on how to clear the immediate problem, but I'm at a loss on how I got into this in the first place.  This database recently changed from no-archivelog with an rman offline backup to archivelog with rman online backups.  The setting of CONTROLFILE AUTOBACKUP FORMAT is virtually identical to all of my other prod databases, and the backup script itself is the same generic script I use for other databases.