So you are clicking edit in a simple module used by your Advanced module (e.g. the blog_posts module inside the blog advanced module)? To debug, I would check out where the 404 error is being outputted in the fuel/modules/fuel/controllers/module.php file (I'm assuming that's what's generating it).
Comments
If that's not it, you may want to check your routes file to make sure the proper route exists for your module:
http://www.getfuelcms.com/user_guide/modules/advanced