I second graff's advice.....create the dialogbox once, and withdraw it. When you need it, deiconify and raise it. Don't destroy it. You can also use the same dialogbox for different purposes, just reconfigure the text messages.

Also in your create_gui sub, you are creating a new mainwindow, this will waste memory if called more than once. So create the $mainwindow once and withdraw it, and when you call the create_gui sub, $mw->deiconify; $mw->raise;