hidden forms and thr handles

Question

i am hiding the form using SetVisibleCore to false, but now i cant get the handle of this form in other application which i am retrieving using EnumWindow its giving me exception "Attempted to read or write protected memory. This is often an indication that other memory is corrupt." an ACCESS VIOLATION EXCEPTION.

so i am searching on 2 ways 1. find out the other way to get handle here we cant use FindWindow cause its not returning any handle 2. find a another way to hide the form but this should be done before loading of the form

so,,,plz help me if anybody can