I'm working on a custom addin with C# + VS2010 + Arc10.1 Pre Release and I don't seem to find the way to make custom icons work for a button that the extension holds and for the extension itself. I pointed the Config.esriaddin appropiate attributes to the files which are both png with alpha transparencies (the icon is 16x16 and the extension img is 64x64). Is there any rule about creating images for icons I'm missing? Why would this not work? Thanks in advance.
I have been struggling with this for a long while too. For example the standard blue dot icon for a button does show, but all my custom icons did not.
By default Visual Studio sets the build action for an image you add to the solution to 'Content'. Apparently this has to be set to 'AddInContent'. After I changed this, all my button images where visible.