Never mind, fixed the issue.
Decided that I needed to find out why Kartris wouldn't run in Integrated Pipeline Mode and after a bit of Googling and some trial and error, it appears that the following line is missing from the web.config file and is required...
<add name="AjaxToolkit" verb="GET,HEAD" path="ScriptResource.axd" type="System.Web.Handlers.ScriptResourceHandler, System.Web.Extensions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
The line of code above needs to go into the <system.webserver><handlers> section. Once added, everything appears to work as expected.
Strange that the line isn't required when running the site locally.