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Home > Success Center > Network Performance Monitor (NPM) > NPM - Knowledgebase Articles > SolarWinds website does not load after upgrading to NPM 12

SolarWinds website does not load after upgrading to NPM 12

Updated June 16, 2016


This article addresses the issue where the SolarWinds website doesn't load after upgrading to NPM 12 and displays the following error:


Unexpected Website Error. Object reference not set to an instance of an object.

Error: <WARN SolarWinds.Orion.Web.ResourceHostManager - Loader Exception
System.IO.FileLoadException: Could not load file or assembly 'System.Web.Http, Version=, 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)
File name: 'System.Web.Http, Version=, Culture=neutral, PublicKeyToken=31bf3856ad364e35'

WRN: Assembly binding logging is turned OFF.


NPM 12 and later


  • This occurs when .NET Framework 4.6 not installed.
  • This occurs also when .NET Framework 4.6 installed, but used SolarWinds License Reset tool to reset licenses on Windows 2008 server environment.


Download and install .NET Framework 4.6. (© 2017 Microsoft, available at, obtained on February 24th, 2017.)


Check the depending services are running

  • Open Server Manager, navigate to IIS section
  • Scroll down to Services part and check the all service Status (Running) and Start Type (Automatic)

Focus on ASP.NET State Service



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