Silverlight Application stopped working for no known reason (no server or code changes made)

Question

I apologize in advance if this question has been answered. I've been searching and didn't see anything similar to my problem.

I build a Silverlight App with a WCF Service to my DB. The application was deployed about three months ago. At that time, I had some users try it out, just to make sure security and functionality worked, more or less as desired.

It has finally gone into UAT (about two weeks ago). I haven't touched the server settings, IIS settings, nor the code since I got the "OK" from the initial testers a few months ago. I haven't even been to the site, as there was no work required nor issues presented.

On Jan 18, a user called the help desk to get assistance in logging into the site. I ASSUME that the issue was resolved, so this would be the last time that someone was able to get to the site.

Now no one can get to the application. Again, I have changed NOTHING. I've spoken with the helpdesk who has told me repeatedly that no changes that they made to fix the user issue should have affected the application (in this case it was a VPN issue).

I get the "this page cannot be displayed" issue, in IE 10 and IE 11. The only thing that has changed on this server in all this time is that Windows server updates have been added. Most of the company uses Windows 7 as their client OS, but one user has Windows 10. He has absolutely no problems getting to the site. The only other way to successfully navigate to the page/site is from inside (logged into) the server.

I have checked all my security settings; I've tried different builds of IE (in case it's a client issue); I've checked my IIS settings; everything is set as it should be. I CAN navigate to the WCF service without issue, just not the application. (ex: http://myapp.mydomain.local/myservice.svc -> works fine; http://myapp.mydomain.local -> does not work)

Sorry to ramble. I wanted to provide as much info as possible. Please help me figure out what I'm doing wrong. Thanks!

Answer 1

So...I found out what the issue was. Some updates were installed at our data center, and one of those updates thought that Silverlight was a threat. It blocked everything.

This was an issue of the developer (me) telling the network guy that something was wrong, while he insisted that it was all on my end of things. When he realized that he could access the application when he didn't go through a firewall, he realized what the issue was (he had some sort of direct tunnel to our data center).

Answer 2

Suggested ways to debug Silverlight problems.

1. Run IE/Firefox (don't use Chrome it is no longer supported) F12 tools and monitor the traffic. It might show that the app is dying due to a database change, cross scripting issue and other what nots to it not being served up. Regardless the F12 network monitor might find other issues...
2. One of the best checks is to see if the silverlight application can run on the server. Remote into the server and launch the page via localhost. If it runs locally on the server but not from the network...start checking firewall etc.
3. Run the program in the debugger on the development box if you can...it might show an exception happening which is the root cause of the program.