SCCM 2012 R2 - Applicaiton Catalogue Error - "Cannot Install or Request Software"

Problem:
You navigate to your application catalogue (http://servername/cmapplicationcatalog/) on a user's workstation. Select an application and click 'install'. Then up pops this error message:

You can browse the list of software in the Application Catalog and view your list of software requests. However, to install or request applications from the Application Catalog, you must use a support version of Internet Explorer and the Configuration Manager client must be installed and properly configured on your computer.

As a follow up, you navigate to the application catalogue log file (c:\Users\<username>\AppData and then search for ConfigMgrSoftwareCatalog.log) and see the followinf messages popping up:

[1][04/15/2015 12:17:40] :ApplicationDetailViewModel.InstallAppProgression-Error:Progress step CanUserinstall: Could not communicate with the client control properly. Error 0x1709.  Debugging resource strings are unavailable. See http://go.microsoft.com/fwlink/?linkid=106663&Version=5.1.30514.0&File=mscorrc.dll&Key=0x1709 0x80041003

Cause: 
Odds are there's something in Internet Explorer which is preventing the Application Catalogue from working correctly. 

Fix:
First check that the sccm html address has appeared in Trusted Sites. Open IE > Tools > Options > Switch to the Security tab > Highlight Sites and then open the Trusted Siters list and check your sccm server has appeared:

This is something which should happen automatically assuming you've defined the CCM Client Settings in the following way in your SCCM Admin Console:

The next thing to check is that Protected Mode isn't on since this will nobble the Applicaiton Catalog and prevent it from working. If your Local Intranet setting looks like this then you'll need to figure a way of changing it (Group Policy being the obvious choice):

Once you disable Protected Mode you should find the Application Catalogue kicks into life and stops throwing up error messages.