erro ao usar o RMAN

Pessoal estou tentando fazer backup usando o rman sendo que executei os seguintes passos:

Primeiro registrei o Database.

RMAN>Register database;

depois ao tentar efetuar o backup apareceu o seguinte erro:

RMAN> run{

2> allocate channel ch_1 device type disk format 'c:\backup\U%';

3> backup database;

4> release channel ch_1;

5> }

allocated channel: ch_1

channel ch_1: sid=15 devtype=DISK

Starting backup at 27-JUL-06

channel ch_1: starting full datafile backupset

channel ch_1: specifying datafile(s) in backupset

including current SPFILE in backupset

including current controlfile in backupset

released channel: ch_1

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

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

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

RMAN-03009: failure of backup command on ch_1 channel at 07/27/2006 15:27:20

ORA-19602: cannot backup or copy active file in NOARCHIVELOG mode

O que estaria causando esse erro?

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