Segmentation Fault?!

[r07f1]

Hey there!

I am in the process of learning Qt4... so i have a simple main window and a dialog... since i only want this dialog object to be created if it hasn't already been... i've coded it's calling slot like this:

void MainWindowImpl::newLocalBackup(){
	if(!nLocalBackup){ 
		nLocalBackup = new NewLocalBackup;
	}
	nLocalBackup->show();
}

void MainWindowImpl::newLocalBackup(){
	if(!nLocalBackup){ 
		nLocalBackup = new NewLocalBackup;
	}
	nLocalBackup->show();
}

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however every time i click the button the program exits giving me a segmentation fault...

what am i doing wrong? how can i debug this type of error? gosh i'm feeling like a noob =x

thanks in advance for your help *