I am using Ext.NET 4.2 and Ext.NET.Mobile 4.1. I pointed to the DLLs directly without using Nuget package.
Here are the config sections:
<extnet scriptMode="Release" cleanResourceUrl="false" theme="Gray" sourceFormatting="false" ...
<extnetmobile scriptMode="Release" cleanResourceUrl="false" sourceFormatting="false"...
I set cleanResourceUrl="false" to avvoid something that seems like a conflict between these modules/handlers:
<system.webServer>
<modules>
<add name="DirectRequestModule" preCondition="managedHandler" type="Ext.Net.DirectRequestModule, Ext.Net" />
<add name="DirectRequestModuleM" preCondition="managedHandler" type="Ext.Net.Mobile.DirectRequestModule, Ext.Net.Mobile" />
</modules>
<handlers>
<add name="DirectRequestHandler" verb="*" path="*/ext.axd" preCondition="integratedMode" type="Ext.Net.ResourceHandler" />
<add name="DirectRequestHandlerM" verb="*" path="*/ext-mobile.axd" preCondition="integratedMode" type="Ext.Net.Mobile.ResourceHandler" />
</handlers>
</system.webServer>
It seems like Ext.NET and Ext.NET.Mobile are using different version of Newtonsoft.Json, so I had to make a binding redirect in web.config to get around it, like this:
<runtime>
<dependentAssembly>
<assemblyIdentity name="Newtonsoft.Json" culture="neutral" publicKeyToken="30ad4fe6b2a6aeed" />
<bindingRedirect oldVersion="0.0.0.0-9.0.0.0" newVersion="9.0.0.0" />
</dependentAssembly>
</runtime>
I am using MVC so I haven't faced the "ItemTag" problem which you are mentioning, at least not yet, but it sounds like you have several namespaces included. Check in your "web.config"s for elements like this:
<pages>
<namespaces>
<add namespace="Ext.Net" />
<add namespace="Ext.Net.MVC" />
They will cause conflicts between Ext.NET and Ext.NET.Mobile if the descending files (forms and views) are using both mobile and classic Ext. My recommendation is to delete them first, and include the needed namespaces in your form.