I'm running into a problem when trying to set the InnerHtml for the resources in the BeforeResHeaderRender method. Setting InnerHtml to e.InnerHTML = "" + e.Name + ""; causes a Microsoft JScript runtime error: Sys.WebForms.PageRequestManagerServerErrorException: An unknown error occurred while processing the request on the server. The status code returned from the server was: 500 The page renders fine, with the text being red, but as soon as there is any interaction with the page, the error occurs. Similar code in the BeforeTimeHeaderRender method causes no problem. Setting ValidateRequest=false in the Page directive fixes the problem, but this is not really a satisfactory conclusion. Any idea why this is occurring only with the resources