I've also tried an icon from the dotNetInstaller samples. This didn't work also.
The icon which i am using has all thinkable resolutions embedded:
256x256 (RGBA and 256 Colors)
48x48 (RGBA, 256, 16 and Mono Colors)
32x32 (RGBA, 256 and 16 Colors)
16x16 (RGBA, 256 and 16 Colors)
I used Axialis IconWorkshop to create it.