App losing dialog modal information

I have an application with has printing capabilities. This application can open a dialog box. In this dialog, I have a "Print" button. When I press this button, I call my application printing function (in fact, printing functions are defined in my MainFrame and I call them from my dialog box). Every thing works fine, but when printing is finished, I can use menus, toolbars, and so on, from my MainFrame, and the dialog box is still there. The MainFrame acts as if it has lost the fact my dialog box is modal.

How can I solve this problem ? I would like my dialog box to be still modal !

Thanks in advance.

Stephane.