Update problems - Unable to insert record error appears when using our form

Hi all

I am currently having a large problem with Oracle Forms Developer. I have coded a LOV to select a customer etc

However, I am unable to update a field --> I keep receiving "unable to insert record" error msg.

This only occurs through the form, we are able to do it the hard way in SQL+

I believe the update code is sound:
update branch
set branchname = :branchname
where branchid = :branchid;
Commit_Form;
clear_form;

If anyone has any ideas I would really like to know

Many thanks
Tom