I have made add-ins before and not had this problem. Not sure what I am doing wrong.
Are you using the Add-in Builder (File > New > Add-in) or the original manual process to create the add-in? Can you examine the contents to be sure that everything is included as you intended?
Also, if you could include screenshots of your add-in's contents, what the View > Add-Ins dialog looks like, those kinds of things, we might be better able to assist you.
Eric