This is because PHP has encountered a fatal error and cannot show any more of the page.

To show the error message that PHP produced, you need to add the debug parameter to your URL. For example, if your current URL is http://www.sourcebans.net/index.php then you can add the debug parameter by changing the URL to http://www.sourcebans.net/index.php?debug=1

If your URL already has parameters, then add debug on the end, like this: http://www.sourcebans.net/index.php?p=home&debug=1

In most cases, the error message will be self explanatory, but if you need help, then post on our forums.