Hello Chandan,
The id parameter in the FM should be the field name for which you want to populate the drop down. And i guess there is no field calledP in your program. Instead you have p_mitar and p_mitarn. So please check my earlier post and put the desired field name of that field, which you want to populate. If you want to populate both, you need to call the FM two times, once with id = 'P_MITAR' and again with id = 'P_MITARN'. Hope you understood what I'm trying to say.
Please let know, in case of issues.
Regards,
Anubhab