I had the same issue and editing the web.config was all that needed to be done. I just wanted to highlight that this may have been from nuget. When i started i had one binding redirect for asp.net MVC
<runtime>
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<dependentAssembly>
<assemblyIdentity name="System.Web.Mvc" publicKeyToken="31bf3856ad364e35" />
<bindingRedirect oldVersion="1.0.0.0-2.0.0.0" newVersion="3.0.0.0" />
</dependentAssembly>
</assemblyBinding>
</runtime>
Then i installed ext.net via nuget and got the following
<runtime>
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<dependentAssembly>
<assemblyIdentity name="System.Web.Mvc" publicKeyToken="31bf3856ad364e35" />
<bindingRedirect oldVersion="1.0.0.0-2.0.0.0" newVersion="3.0.0.0" />
<assemblyIdentity name="Newtonsoft.Json" publicKeyToken="30ad4fe6b2a6aeed" />
<bindingRedirect oldVersion="1.0.0.0-4.5.9" newVersion="4.5.10" />
<assemblyIdentity name="Ext.Net.Utilities" publicKeyToken="2c34ac34702a3c23" />
<bindingRedirect oldVersion="0.0.0.0-2.0.1" newVersion="2.1.0" />
<assemblyIdentity name="Transformer.NET" publicKeyToken="e274d618e7c603a7" />
<bindingRedirect oldVersion="0.0.0.0-2.0.0" newVersion="2.1.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="Transformer.NET" publicKeyToken="e274d618e7c603a7" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-2.1.1.22883" newVersion="2.1.1.22883" />
</dependentAssembly>
</assemblyBinding>
</runtime>
I'm not 100% on how this config section is handled but from an xml point of view it doesn't seem logical or it would be difficult to handle this config section and try to figure out what redirect applies to which assembly. So after applying your fix I ended up with the following and i didn't get the exception.
<runtime>
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<dependentAssembly>
<assemblyIdentity name="System.Web.Mvc" publicKeyToken="31bf3856ad364e35" />
<bindingRedirect oldVersion="1.0.0.0-2.0.0.0" newVersion="3.0.0.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="Newtonsoft.Json" publicKeyToken="30ad4fe6b2a6aeed" />
<bindingRedirect oldVersion="1.0.0.0-4.5.9" newVersion="4.5.10" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="Ext.Net.Utilities" publicKeyToken="2c34ac34702a3c23" />
<bindingRedirect oldVersion="0.0.0.0-2.0.1" newVersion="2.1.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="Transformer.NET" publicKeyToken="e274d618e7c603a7" culture="neutral" />
<bindingRedirect oldVersion="0.0.0.0-2.1.1.22883" newVersion="2.1.1.22883" />
</dependentAssembly>
</assemblyBinding>
</runtime>
So all i'm trying to highlight here is that when i install from nuget i got a funky looking config section that needed cleaning so i'm not sure if this helps narrow down what is happening.
MB