Assign Leads

Assign Leads

Hi,
I   wrote   a   function   to   assign   Leads .   I use   the   crm.updaterecord   function

crmUpd = zoho.crm.updaterecord("LEADS",Rta.get(0).toString(),{"Lead Owner":"Alejandro Enrique"});

The  update  was   successful ,   but   the  owner not change . The "Modified By" field is updated.
The user "Alejandro Enrique" exists and Rta.get(0) is a valid ID.

That   is   wrong ?

Regards 
Alejandro