The ScreenShots that I got to the AppHub associated with my application were transparent PNGs
As well, with major problems > > small solutions. In my case, as the treatment of images I do local with IrfanView as a viewfinder and Paint.Net as editing tool. If I have more advanced problems I turn to Expressión Blend or one who knows.But well, in this case in particular, the solution consisted in
- Open the PNGs with IrfanView
- Perform a "Save As" in PNG format
- Uncheck the option "Save Transparent Color"
In 10 days about see if you like this or not the people of AppHub.
Greetings @ La Finca