convert tablespace的限制

RMAN> convert tablespace ORA_data to platform 'Microsoft Windows x86 64-bit' format='/dmp/transport_win_%U'; 

Starting backup at 19-APR-11
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: sid=1000 devtype=DISK
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of backup command at 04/19/2011 12:09:50
RMAN-06599: tablespace ORA_data is not read-only

RMAN>