Hi Giulio,
The UDF form is not really easy to manage: depending on the version, it doesn't exist if not open (up to 8.82 I('m sure, not for V9.0) or do exist.always (I'm sure for 9.1 but not for 9.0).
In all cases, the content of this form can be managed by setup which would be (opens the form, Tools / Customization Tools / Settings) a lot easier to do...
Regards,
Eric