Original User: tereshenkov
I am not sure what the problem is, but try the following:
1. Delete the uploaded add-in from the Builder > Settings.
2. Upload it again and make sure the .xap file is accessible to the machine from which you use Builder.
3. Restart the IE and open the Builder again. The QueryAddIn should show the description (Settings menu).
4. Clear the IE cache if it still doesn't show up.
5. Install SL Viewer 3.1 (I am pretty sure the add-in is supposed to work with 3.0 too, but I am personally running 3.1) and run the upload again.