Could not load System.Web.Cors in Owin Startup.cs

Question

I have a .Net 4.5.1 application using Web API 2 and running in my local Azure Emulator. I have some OWIN components installed and in my Startup.cs file within the Configuration(IAppBuilder app) function I have the following code block and the last line causes an exception:

HttpConfiguration httpConfiguration = new HttpConfiguration();
WebApiConfig.Register(httpConfiguration);
app.UseWebApi(httpConfiguration);
app.UseCors(Microsoft.Owin.Cors.CorsOptions.AllowAll);

This line is causing an exception "Could not load file or assembly 'System.Web.Cors, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies."

I'm having trouble figuring out why NuGet didnt' install this if it is a dependency. Additionally I'm not able to find a corresponding dll already installed to add a reference myself, nor the correct NuGet package to install to provide said dll.

Has anyone experienced a similar issue? If so, perhaps you could point me in the right direction.

Answer 1

This is surely coming cause of your DLL version is different OR DLL is missing on that environment.

Few steps you require to check:

• Cors DLL should be there in your BIN directory [On Azure]

• If it's there then Version of DLL deployed on server and your local both should be same. [You can check in properties]

• If your version of Cors DLL higher on Azure server, compare to local one then you can

<dependentAssembly>
   <assemblyIdentity name="System.Web.Cors" publicKeyToken="31bf3856ad364e35" />
   <bindingRedirect oldVersion="1.0.0.0-5.0.0.0" newVersion="5.0.0.1" />
</dependentAssembly>

Your new version could be your DLL version which are available into the BIN directory.

Answer 2

Have you tried Microsoft.Asp.Net.WebApi.Cors at nuget? https://www.nuget.org/packages/Microsoft.AspNet.WebApi.Cors/5.2.2 It's not a dependency for the Cors package because it's for webapi and the only microsoft.owin.cors dependency is on the base microsoft.asp.net.cors (other than the owin packages).