I'm not seeing an error during use of the site, but I'm getting many errors in the system log.

The controller for path '/undefined' was not found or does not implement IController

System.Web.HttpException (0x80004005): The controller for path '/undefined' was not found or does not implement IController. at System.Web.Mvc.DefaultControllerFactory.GetControllerInstance(RequestContext requestContext, Type controllerType) at System.Web.Mvc.DefaultControllerFactory.CreateController(RequestContext requestContext, String controllerName) at System.Web.Mvc.MvcHandler.ProcessRequestInit(HttpContextBase httpContext, IController& controller, IControllerFactory& factory) at System.Web.Mvc.MvcHandler.<>c__DisplayClass6.<BeginProcessRequest>b__2() at System.Web.Mvc.SecurityUtil.<>c__DisplayClassb`1.<ProcessInApplicationTrust>b__a() at System.Web.Mvc.SecurityUtil.<GetCallInAppTrustThunk>b__0(Action f) at System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Action action) at System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust[TResult](Func`1 func) at System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, Object state) at System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContext httpContext, AsyncCallback callback, Object state) at System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData) at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

I've seen this kind of error when a js file is referencing something. Ie: if it's looking for a secodary js file using a / when it's being used inside a sub folder.

My guess would be that you've got some javascript that is dynamically referencing something incorrectly, so trying to redirect to /undefined which doesn't exist

Greg