the internal refresh rate change is not working in windows 7.
when mediaportal tries to switch the refreshrate nothing happens.
image gets black, and you hear the audio of the video playing.
no OSD displayed and according to the info provided by the TV, the refreshrate did not change.
as soon as you stop the polayback, the MP GUI is displayed nicely again.

it seems that microsoft changed the API.

using the action field to launch i.e. "Display Changer" to change the refreshrate is working like a charm

h4. Additional Information
http://forum.team-mediaportal.com/mediaportal-releases-315/w7-refreshrate-changer-causes-bsod-68745/