TSPITR via RMAN in a Data Guard Environment

I am trying to do a Tablespace-Point-In-Time-Recovery in a Data Guard Environment.

On the Primary server I backup the control files, spfile and archivelogs with RMAN (catalog). On the Physical Standby I dump additionaly to the mentioned files the datafiles via following commands:

RECOVER COPY OF DATABASE WITH TAG 'ORA\$OEM_LEVEL_0';
BACKUP DEVICE TYPE DISK INCREMENTAL LEVEL 1 FOR RECOVER OF COPY WITH TAG 'ORA\$OEM_LEVEL_0' DATABASE;

When I try to recover a test tablespace on the Primary point-in-time I get a ORA-01180 Error in RMAN:

RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of recover command at 03/16/2009 14:59:57
RMAN-03015: error occurred in stored script Memory Script
RMAN-06136: ORACLE error from auxiliary database: ORA-01180: can not create datafile 1
ORA-01110: data file 1: '/oracle/adm/data/system01.dbf'


This file is the system tablespace of my primary database. It has the correct permissions and is a regular file. Anyway, I am wondering why the TSPITR process wants to (re-)create that. The auxiliary database is created in /oracle/adm/dbflash/tspitr and if I understood correctly, the TSPITR is only creating a auxiliary database and importing from that into the original database.

Another strange thing is, that when I am doing a full RMAN-backup with "backup database" on the Primary I am getting following error:

RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of recover command at 03/16/2009 15:47:25
RMAN-03015: error occurred in stored script Memory Script
ORA-19571: datafilecopy recid 97 stamp 681661326 not found in control file
ORA-19600: input file is datafile-copy 97 ()
ORA-19601: output file is datafile-copy 0 (/oracle/adm/data/mstroech_test.dbf)

Any ideas or experiences with incremental backups and TSPITR?

Thank you in advance!