restoring tablespace

Hello,

I built up a test case and trying to restore my tablespace but unable to do so since it shows below error.After taking backup of tablespace tb1 I dropped tablespace and now trying to restore.

RMAN> backup tablespace tb1;

Starting backup at 06-MAR-15

using channel ORA_DISK_1

channel ORA_DISK_1: starting full datafile backup set

channel ORA_DISK_1: specifying datafile(s) in backup set

input datafile file number=00005 name=/lvsnap/newdb/datafile/NEWDB/datafile/o1_m                                                                                                                     f_tb1_bhmxh4mw_.dbf

channel ORA_DISK_1: starting piece 1 at 06-MAR-15

channel ORA_DISK_1: finished piece 1 at 06-MAR-15

piece handle=/lvsnap/newdb/arc/NEWDB/backupset/2015_03_06/o1_mf_nnndf_TAG2015030                                                                                                                     6T135311_bhmxwqjz_.bkp tag=TAG20150306T135311 comment=NONE