Error when clicking item in 404 Not Found view

[StateBarofArizona]

An unhandled exception occurred System.Web.HttpUnhandledException (0x80004005): Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> System.InvalidOperationException: Sequence contains more than one matching element at System.Linq.Enumerable.Single[TSource](IEnumerable1 source, Func2 predicate) at InfoCaster.Umbraco.UrlTracker.UI.UrlTrackerManager.LoadDetail(Object dataKey, String secondKey) in D:\kipusoep\Documents\GitHub\UrlTracker\UI\UrlTrackerManager.aspx.cs:line 410 at System.Web.UI.WebControls.GridView.OnSelectedIndexChanged(EventArgs e) at System.Web.UI.WebControls.GridView.HandleEvent(EventArgs e, Boolean causesValidation, String validationGroup) at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) at System.Web.UI.Page.HandleError(Exception e) at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) at System.Web.UI.Page.ProcessRequest() at System.Web.UI.Page.ProcessRequest(HttpContext context) at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)