Hvorfor kan jeg ikke enable trace

Når jeg indsætter Trace="true" i min " <%@ Page " så får jeg en fejl: "Object reference not set to an instance of an object." Hvorfor?

Her er min stacktrace:
[NullReferenceException: Object reference not set to an instance of an object.]
  System.Web.Handlers.TraceHandler.CreateControlTable(DataTable datatable) +2442
  System.Web.TraceContext.Render(HtmlTextWriter output) +219
  System.Web.UI.Page.ProcessRequestEndTrace() +2056078
  System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +213
  System.Web.UI.Page.ProcessRequest() +86
  System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context) +18
  System.Web.UI.Page.ProcessRequest(HttpContext context) +49
  ASP.templates_underkategori_aspx.ProcessRequest(HttpContext context) in c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\forlaget\34c03813\e837ed48\App_Web_sn-armhc.0.cs:0
  System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +303
  System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +64