I am not sure what else to suggest, Al, except some basic things that you may have already tried.
Try creating a brand new button with a condition such as
condition="E3_SingleFolderSelectedCondition"
Don't even add any code to it and save it as the default name that MS Visual gives the solution.
Does the new button start out greyed out when you start up AGX with the default map?
Try deleting the current default map, then manually add in the test button yourself to the new default map that AGX automatically creates the next time you start the program.
As I said, the condition in AddIns.xml works on my system, so I can only assume it should work on yours if we can get things basic enough.
What version of Windows and Visual Studio are you running?
Norm