ChrisW67 thanks for your response.
i will try to clarify why I'm using exec there.

The intended usage is something like this.

The user clicks on the menu.
A form is created where a list of the products is show wich has a button to create a new one.
That new form should block the product list to prevent the user from clicking tome other stuff on THAT parent form only. not to prevent him or her to open other unrelated things from the menu.

With mi current approach the third form appears outside the mdi area.
i don't know what are you referring to when you say that it breaks your test program, here compiles and runs fine, but maybe as I'm just a beginner something is not behaving as it should and I can't notice.

i think i will go with the signal/slot approach and prevent the user from using the intended parent widget by hiding it.