PTR set until time problem.

I'm trying to do a point in time recovery.  What is wrong with this?

RMAN> RUN {
2> SET UNTIL TIME 'SEP 28 2010 04:00:00';

....
3> }

executing command: SET until clause
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of set command at 09/28/2010 08:36:32
ORA-01858: a non-numeric character was found where a numeric was expected

Thanks - JR