You could be running into the issue simply because the order you tried things. To get the image to display you should do the following (in order):
1) Open LaunchBox, go to Tools > Manage > Platforms.
2) Select the platform in question and press edit
3) In the form that appears the right hand side shows images assigned to the platform. Verify that a logo is present, if there isn't one add it by using the Add Image button or dragging the image to the window. When adding an image using either method make sure to assign the image type to clear logo by selecting the text in that control and then selected the Clear Logo image type from the menu that appears
4) Press OK to save changes, then close LaunchBox
5) Open Big Box, then go to the system menu (press back) and then to Options
6) Go to the Image cache section and clear your platform image cache
7) Return to your wheel and you should see the image as desired