This link : https://helpcenter.websitex5.com/de/post/192257

Hi Nicole, 

please either delete the config.xml file you can find in c:\Users\ Your Windows username \AppData\Local\Incomedia\WebSite X5 v15- Professional or edit it like this:

<IPAddress>127.0.0.1</IPAddress> 
<PortNumber>8080</PortNumber>

You should be able to temporarly solve the issue this way. Still, we have reported it to the developers anyway, so I will inform you when a better solution will be available.

I wish you a lovely day. Kind regards

Problem solved