To locate the exact problem, please call do the following steps:
1) Open ISPConfig and login, you will see a URL that looks similar to this:
Now change it to:
and load the URL in the browser. Then select to view the sourcecode of the page, make a .zip out of it and post it here. The source contains the titles of all of your websites, if you feel better to not post them here, you may send it to me as PM.