I was looking at an issue posted in the forum about not able to debug server controller for admin extension. Couldn’t really figure out what could be the root cause, as the controller should get loaded and return data (default expectation). Getting a 404, strange.

Looked at the issue over a remote session and we found the root cause of the issue from event log.

LogName: Microsoft-WindowsAzurePack-MgmtSvc-AdminSite/Operational Error:Unhandled exception: FileLoadException: Could not load file or assembly 'System.Web.Mvc, Version=5.2.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

For some reason, the NuGet package on the development environment updated the project to MVC 5.2 and the WAP Admin site was not loading the extension DLL because of the failed dependency.

Thought others might also run into this issue (knowingly or unknowingly) . As a quick resolution, we rebuilt the admin extension against MVC 4.x libraries and it started working.