Don't know how much of this is relevant but:

I have a class derived from 'Form' - very simple modal dialog, no datasession, just one property bound to a two option radio button.
I have a Form based on this class with no overrides.
I instantiate the Form from a 'main' form with 'DO FORM xxx TO rdiChoice'
The xxx form never appears and I get a error 12 (variable is not found)
I've add code that verifies that the Form.Load() and Form.Init() both execute without error.
I've put a Try/Catch around 'DO FORM xxx TO rdiChoice' but no exception is thrown.

Now the odd bit:

When running the EXE on my machine everything works as expected.
On a testers machine I get the above behaviour.

Seems as if my EXE is successfully accessing something that's no available on the production version.
Only thing I can think of is that the form icon isn't being found - but it looks OK and the same thing works on other forms.

What should I be looking at ?