Nevermind. ......
... Can anybody give me a hint at what I'm doing wrong? ...
In the first step I would suggest to download the attached package and to extract the content to a separate folder. Now, please open an elevated command prompt and try to start the monitor application with the parameters described in the manual. Please try it with your computer name, your IP address and a lower refresh rate. Please observe the behavior of the status icon and report your results.
"HTPCInfo TVServer Monitor.exe" 192.168.1.250 10
Rightclicking->Details still correct, showing all TV-cards with correct status.TVServer: 192.168.1.250 - Searching ...
"HTPCInfo TVServer Monitor.exe" osksa-PC 192.168.1.250 10
"HTPCInfo TVServer Monitor.exe" localhost 30
Thank you, barneh, I checked and I have the lastest version of the plugin, 1.13.1.0. Note that I am talking about the TVServer Monitor (tray) application, which has its own versioning and is currently on 1.1.1.0.The latest version are of the plugin are 1.13.1.0. So please use the Mediaportal Extensions Manager for downloading plugins!
This will help you to have you're plugins up to date and installed right!