Forms :: Create Directory With Oracle Form PL/SQL

i want to know how to create directory or folder which use pl/sql coding in oracle developer suite10g

my problem is when i use this code

trigger WHEN-BUTTON-PRESSED

EXECUTE IMMEDIATE 'CREATE OR REPLACE DIRECTORY'||'C:RESTAURANT';

IT'S ERROR WITH "Error591 this feature is not supported in client-side programs"

I used to use function with webutil that's webutil_file.create_directory('c:RESTAURANT');

trigger WHEN-BUTTON-PRESSED

WEBUTIL_FILE.CREATE_DIRECTORY('c:RESTAURANT');

BUT STILL HAVE ERROR WITH "Error 221 'CREATE_DIRECTORY' is not a procedure or is undefined "

How to create directory with pl/sql that's use in oracle form in trigger when-button-pressed or how to use function webutil_file.create_directory();