RMAN DUPLICATE FOR STANDBY FROM ACTIVE DATABASE fails

Question

Hello
I'm trying to use RMAN DUPLICATE to create a standby database using Oracle 11.2.0.3 with PSU 6 on HP-UX.
Primary is 2 node RAC. Standby is also 2 node RAC.
Standby database instance is started in nomount mode.
I use:
duplicate target database for standby from active database
  spfile
  <some spfile parameters>
with PFILE I get:
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of Duplicate Db command at 10/01/2013 12:41:13
RMAN-05501: aborting duplication of target database
RMAN-03015: error occurred in stored script Memory Script
RMAN-03009: failure of sql command on clone_default channel at 10/01/2013 12:41:13
RMAN-11003: failure during parse/execution of SQL statement: alter system set spfile= '/opt/oracle/db11203/dbs/spfileCU1.ora'
ORA-02097: parameter cannot be modified because specified value is invalid
ORA-01565: error in identifying file '/opt/oracle/db11203/dbs/spfileCU1.ora'
ORA-27037: unable to obtain file status
HPUX-ia64 Error: 2: No such file or directory
With SPFILE I get;
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of Duplicate Db command at 10/01/2013 13:06:34
RMAN-05501: aborting duplication of target database
RMAN-05537: DUPLICATE without TARGET connection when auxiliary instance is started with spfile cannot use SPFILE clause
But I do have RMAN connexion to target database.
Thanks for your help.

Answer 1

Here is the output beginning of the script which clearly shows that I'm always connected to target database:
Recovery Manager: Release 11.2.0.3.0 - Production on Tue Oct 1 13:05:47 2013
Copyright (c) 1982, 2011, Oracle and/or its affiliates.  All rights reserved.
connected to target database: CU (DBID=1143962925)
connected to auxiliary database: CU (not mounted)
RMAN> set echo on
2> run
3> {
4>  configure device type disk parallelism 10;
5>   allocate channel pr1 type disk;
6>   allocate channel pr2 type disk;
7>   allocate channel pr3 type disk;
8>   allocate channel pr4 type disk;
9>   allocate channel pr5 type disk;
10>   allocate channel pr6 type disk;
11>   allocate channel pr7 type disk;
12>   allocate channel pr8 type disk;
13>   allocate channel pr9 type disk;
14>   allocate channel pr10 type disk;
15>   allocate auxiliary channel st1 type disk;
16>   allocate auxiliary channel st2 type disk;
17>   allocate auxiliary channel st3 type disk;
18>   allocate auxiliary channel st4 type disk;
19>   allocate auxiliary channel st5 type disk;
20>   allocate auxiliary channel st6 type disk;
21>   allocate auxiliary channel st7 type disk;
22>   allocate auxiliary channel st8 type disk;
23>   allocate auxiliary channel st9 type disk;
24>   allocate auxiliary channel st10 type disk;
25>   duplicate target database for standby from active database
26>   spfile