Chm file freeze the application when Url or Print buttons were clicked

When I open help file from my Windows Forms application I'm using this code.

    public static void ShowHelp(string constant)
    {
        Help.ShowHelp(dummyFormForHelp.Value, CHMFile, HelpNavigator.Topic, constant);
    }

It works fine except when I click on GO>URL... or Print button in the help file. [

I get no messages and the app and chm file don't response at all. And I need go to task manager and kill the process. I have no idea what it is.

I tried to open the same file using the same code from the simple Windows Form application with only one form and everything was perfect. So I think something wrong in my application.

What can cause such issue? It's a big enterprise application with a lot of screens.