Because some countries have localized number formatting like this 1 200,00 & not 1.200,00 or 1,200.00 the adjustment for pixel ratio fails & causes wrong thumbnails & sometime black screen in MyTV & MyVideos.

Reproduce:
Use localized settings like Language: Norwegian & Unicode: Norwegian.
Go to MP home select Settings -> Screen Calib. ->Screen Calib. Then calibrate the pixelratio to 1,15. Then go to MP home & exit.
Open the Calibration(screen resolution)).xml in mp root, it shows the correct pixelratio.
Do the above one more time, the Calibration(screen resolution).xml now shows 115.
You will also see that the second time you enter screen Calib. the pixelratio box is wrong.

h4. Additional Information
I'll try to explain whats happen in Norwegian versions:
Ref: Settings.cs, line 123 -> 129:

        float test=123.456f;
        string tmp=test.ToString();// In Norwegian this will be 123,456
        bool useCommas = (tmp.IndexOf(",") >= 0); //This will turn to true
        if (useCommas==false)
          strValue = strValue.Replace(',', '.'); //Nothing it's replaced, this would have fixed it if useCommas = true.
        else
          strValue = strValue.Replace('.', ','); //Nothing it's replaced

Links to forum:
http://mediaportal.elite-squad.net/forum/showthread.php?t=415
http://mediaportal.elite-squad.net/forum/showthread.php?t=397