incomplete point-in-time recovery

Hello.

I am trying to restore a lost partition of one table. To do that I am doing an incomplete point in time cross-node recovery. I have restored the system, sysaux, undo as well as the tablespace where my table is residing as of the time before the partition was dropped. I have also restored the archived logfiles and the controlfile for an appropriate time.  Now I am trying to recover the datafiles as follows:

sql 'alter session set nls_date_format="mm-dd-yyyy hh24:mi"';
set until time '07-21-2009 20:00';
allocate channel t1 type 'SBT_TAPE';
allocate channel t2 type 'SBT_TAPE';