I installed Windows Azure SDL V 1.3, then I tried to create a Hello World Azure Application.I pressed F5 and got the error as below: I tried Ctrl+F5 to run without the debugger and did not get the exception above but instead got a service unavailable error in the browser. On this particular exception I found a very good discussion hereOption 1First suggestion was to check whether there are two folders in C:\Windows\Microsoft.NET\Framework64 for V4.0 and rename one of the folders. I checked and I found I had only one folder for v4.0.30319 so this suggestion was not relevant to me. Option 2Second suggestion was to open the command prompt and run aspnet_regiis.exe â€“r. I tried and again I was not lucky. Option 3Third suggestion was to change the target framework from V4.0 to v3.5. I did that and was unlucky once again. Option 4Fourth suggestion was to delete the Sites element from the ServiceDefinition.csdef file. I was unlucky once again. Option 5Fifth option was to test whether a normal web Application with target framework 4.0 is getting published successfully in IIS or not? I tried that and I was able to publish. So my IIS was working fine. I got frustrated and restarted and system and found everything working, I did not get that debugger exception. I have no idea what happened but this was my experience with this popular exception.