When setting the background to transparent it can be difficult to click on the buttons. This is by design to allow users to create their own button images and use those images by themselves to define the shape of the button by setting the border/background/hover colors to transparent as well. But what about the default icons/settings that come with RadialMenu?
To make it easier to click on things, go to the color settings for the background and then click 'Advanced' at the bottom, then change the transparency to an -almost- transparent value using one of the following methods:
1. Move the bottom slider to 1 or type 1 in the box next to it.
2. Enter this value in for the color "#01FFFFFF".
The button will appear transparent but it's not actually completely transparent. The entire button will now react to clicks.