You are trying to change a user which does has not been created yet? Perhaps if you react to the message of the return then you will see that.
Anyway, the parameters are a tables parameter of the BAPI and you are not importing any data into the table. You are only populating defaults and logon and address data...
I think I am a bit closer now to understanding now why SAP deprecated these exits... :-) Have you seen the new BADIs? (Class SUID_IDENTITY). But you are ina fix on SOLMAN as you cannot go to higher than 7.02 at the moment... :-(
Cheers,
Julius