I have a little problem. After sending a message, I will not be forwarded (as before it was working) to the same page with a confirmation text. Now a blank window will be shown (not using my page template.
I don't see that problem on the site you mentioned. Maybe you modified the settings.
When a blank page is displayed by Joomla it usually means you have some errors in the code and you can activate displaying the error messages ( in Global configuration, "Server" tab, "Error Reporting" field ).
That usually clarifies what the problem is.