I am working with an ASP.net MVC4 project with WebAPI, and upgraded/installed a number of nuget packages (and stupidly did not test after each one). When the dust settled, I tried to load an API page in my browser and got the following error message:
"Could not load type 'System.Web.Razor.Parser.SyntaxTree.CodeSpan' from assembly 'System.Web.Razor"
Eventually, I was able to resolve the error by removing the following from my web.config and app.config files:
<!-- Begin Remove -->
<assemblyIdentity name="System.Web.Razor" publicKeyToken="31bf3856ad364e35" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-22.214.171.124" newVersion="126.96.36.199" />
<!-- End Remove -->
I would guess that one of the packages that I installed added this reference, which had a conflict with a different version of the same assembly in the GAC. In any event, it fixed the error (and did not cause any apparent new errors). Posting in case it may help you out with a similar error.