Personalization in a form

Hello

I'm trying to set the UPDATE_ALLOWED property of an item in the Assets form (Projects -> Assets)

I tried using all the triggers as below, but still it does not seem to set the item to non updateable. What happens is, when its on a new record or when I try to create a new record, the item becomes Updateable.

WHEN-NEW-FORM-INSTANCE

WHEN-NEW-BLOCK-INSTANCE

WHEN-NEW-RECORD-INSTANCE

WHEN-NEW-ITEM-INSTANCE

Any help ?

Thanks

Len