Hey Zarsie,
Can be a number of different reasons for this, but in the images you attached only two of the 3 inputs are being used by the select node. Looks like your empire set may not be returned from the collapsed code into the select node.
If you still seem to be getting this error you can reply with another image of your “Get Card Data” function changes so we can have a look. If you are using UE4.16 > you should also be able to change this function to be like suggested in post #132 of this thread to be easier to add your card sets to reduce the hassle of adding your new card sets.
Also, one of the more common reasons for this would simply be to open the main menu/ deck builder if you haven’t done so already. Let me know