Silverlight Applications (SCCM Application Catalog) Stop Working If Silverlight Not Up To Date

Yeah... so... had a weird thing happen with our App Catalog.  It just up and stopped working.  It was working Friday, not working today.

Of course the Internet was full of useful information on the App Catalog such as how to install it, how to troubleshoot it, what this or that error in the logs means, etc, etc, etc.  What it wasn't full of was anything that was relevant to my symptoms.

My symptoms were:

• Site Status shows both Application Catalog web service point and Application Catalog website point as Critical.
• Component Status shows both components running and green.
• Logs have no errors for either component.

Yeah... not much to go on with those symptoms.

I was reading over Microsoft's Technet article on how the App Catalog works and it said that it will install Silverlight 5 when it installs.  Simply out of curiosity I wondered what the latest version of Silverlight was so I went over to the Silverlight site to find out.

Low and behold a message at the bottom of my web browser... "Silverlight has been blocked because it is not up to date" (or something very similar) and an "update" button.  At this point, knowing that Silverlight is required for the App Catalog, and now knowing that Silverlight is being blocked by... Silverlight? Browser?... whatever, something Microsofty... I clicked "Update".

Sure enough, about 15 seconds later my App Catalog is back online.  So, there you go... I'm guessing this will apply to any Silverlight application but it definitely applies to SCCM Application Catalog.