The Fix

If you look at the URL it's trying to load you'll notice that the URL has the following /?ACT={AID:Channel:combo_loader}

This is the root of the problem. ExpressionEngine is meant to take the AID bit and find a unique number for the action from the database. It showing {AID:Channel:combo_loader} means it hasn't found one.

It's an easy fix though! Head into your database and in the exp_actions channel insert a new entry.

Leave the Action ID blank, make the class "Channel" and the method "combo_loader" (notice how that matches up with the AID error). Leave the 'csrf_exempt' field empty and go!

When you next refresh the page this problem should be fixed.