And what is the help that you need?
I can guess but I can also guess wrong.
And how have you set up the relationship between Invoices and Customers?
Is this adapted from a starter solution?
Yes it is adapted from the starter solution. What i want to do is when you browse customers accounts, if you come across an account with past due balance, the pop up dialog will be triggered when you access the layout..
When you say 'Browse', how are you browsing? Scrolling the mouse in Form View? If so, you want to trigger your script with OnRecordLoad
How is the field "Due Since" defined?