Do you receive the dialog box of the user name and password, once you open the forms runtime ?
if yes : this means you get connected and once after, you will be disconnected, which could be because of a network error, or because someone run an SQL*PLUS script that creates the table PRODUCT_USER_PROFILE, and inserted some records there that prevents you from connecting to the database through Forms, in this case check the mentioned table.

if no : this means that you have a trigger on the forms level called "on_logon" this trigger is fired instead of the dialog box, of user name and password, so the form is open successfully without being connected, and when it tries to execute the first SQL statement, it finds that it is not connected.
so check if you have a code on the trigger "on_logon"
either correct it or delete the trigger.