i have the following issue. I have a custom icon for my custom button in the ribbon bar implemented, but this icon can not be rendered correctly. This icons is displayed as . And I don't know how to solve this problem. My VisualStudio 2013 solution tree looks like this:
And my Elements.xml:
I also tried
_layouts/Images/CustomRibbonProject/Symbo_16x16.png, but neither works.