The error I received at a client site was:-

RMAN> restore database;

Starting restore at 17-AUG-11

using target database control file instead of recovery catalog

allocated channel: ORA_DISK_1

channel ORA_DISK_1: sid=1482 devtype=DISK

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

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

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

RMAN-03002: failure of restore command at 08/17/2011 18:01:01

ORA-01220: file based sort illegal before database is open

I was able to continue with the restore once I ran the following:-

SQL> show parameter sort

NAME                                 TYPE        VALUE

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

nls_sort                             string

sort_area_retained_size              integer     0

sort_area_size                       integer     37000

SQL> show parameter workarea

NAME                                 TYPE        VALUE

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

workarea_size_policy                 string      MANUAL

SQL> alter system set workarea_size_policy = AUTO scope=spfile;

System altered.

SQL> alter system set sort_area_retained_size = 256000 scope=spfile;

System altered.

SQL> alter system set sort_area_size = 256000 scope=spfile;

System altered.