call_Form ('MVLAUDSIGNON',NO_HIDE,DO_REPLACE, NO_QUERY_ONLY) -replacement in R12

call_Form ('MVLAUDSIGNON',NO_HIDE,DO_REPLACE, NO_QUERY_ONLY)  in custom PLL is giving error FRM-40010 Cannot read form.

I changed the syntax as below:

fnd_function.execute(function_name => 'MVLAUDSIGNON'

                                 ,open_flag => 'Y'

                                 ,session_flag => 'Y'

                                 ,other_params => NULL);

Now I am getting APP-FND 01926- custom event raised unhandled exception, non oracle exception.

Can anyone quickly help.