This is probably a problem with your paths on the server. You may need to configure the Ext.loader for your paths and you may need to add an entry for appFolder in the app.js file after you save your project in Architect.
If the server needs to find you application at /x/Myapp/app/ you need to add
appFolder: "/x/MyApp/app/" in another editor before you run your project on your server. Don't do this in architect, it will screw up all of your folders.
c is not a constructor seems to always mean (at least what I've seen) that Extjs can't find the files it needs to create the app.