ASP.NET MVC tries to load older version of Owin assembly
I updated to OWin 3.0.1 and that fixed the problem:
Tools -> NuGet Package Manager -> Manage NuGet Packages for Solution
I searched for the references in the list (under NuGet.org) and installed new references for Microsoft.Owin as well as Microsoft.Owin.Security, Microsoft.Owin.Security.Google, Microsoft.Owin.Security.Facebook etc.
I then checked the version number in my packages.config and Web.Config file and found that this had updated correctly:
Packages.config example:
<package id="Microsoft.Owin.Security.Google" version="3.0.1" TargetFramework="net45" />
Web.Config example:
<assemblyIdentity name="Microsoft.Owin.Security" culture="neutral" publicKeyToken="31bf3856ad364e35" />
<bindingRedirect oldVersion="0.0.0.0-3.0.1.0" newVersion="3.0.1.0" />