The Problem
Standard promoted actions
Customized promoted actions
You create a custom master page. Deploy it through Visual Studio, set it to your custom/default master page and suddenly you get "Unauthorized 401" all over the place. I looked around and found out that this only happened when having the "Minimal Download Strategy" site feature enabled and SharePoint run the request through the start.aspx page.
So what to do ? Turn off the feature? No that is not an option. It is a great performance enhancement that comes along with SharePoint 2013 so it should NOT be turned off! Keep it enabled and found out the real source of your problems instead.
The Solution
In my case I noticed that I had been moving the promoted action buttons and did not put it inside of an SharePoint:AjaxDelta control. You have to put user controls and such which will have data that may change if you don't want to get that error to occure when having the "Minimal Download Strategy" site feature enabled. Otherways SharePoint will throw this as it doesn't have the permissions to pull out the data in the asyncronical request.
Do you get the same error but you can't fix it with the Ajaxdelta control ? Please comment or send me a line, I would be very interested.
//M