Initial User Selection and Xpath

Hi,

I try to select an initial user by Xpath expression.
I have a form with a field name binding with commonname from the edcprincipalentity table, a field userid binding with id from the same table.
I have in my process variables username (Type string)and userid (Type string) and i try to map them with my fields but they are still empty.
I try to send a form fill by a user to a user specify in the form by fill the xpath expression in initial user selection with :
- /process_data/@iduser (doesn't work)
- /process_data/@username (does'nt work)
-
/process_data/InitForm/object/data/xdp/datasets/data/RECORDS/RECORD/co mmonname
(does'nt work)
- /process_data/InitForm/object/data/xdp/datasets/data/RECORDS/RECORD/i d (doesn't work)

Thank you for helping me.

Sorry for my English.