I researched this on the Internet and modified my code by:
changing my web.config file by:
When this didn't work I added the the following method (coded sourced from Internet):
protected override void Render(System.Web.UI.HtmlTextWriter writer)
{
System.IO.StringWriter stringWriter = new System.IO.StringWriter();
HtmlTextWriter htmlWriter = new HtmlTextWriter(stringWriter);
base.Render(htmlWriter);
string html = stringWriter.ToString();
string[] aspnet_formelems = new string[5];
aspnet_formelems[0] = "__EVENTTARGET";
aspnet_formelems[1] = "__EVENTARGUMENT";
aspnet_formelems[2] = "__VIEWSTATE";
aspnet_formelems[3] = "__EVENTVALIDATION";
aspnet_formelems[4] = "__VIEWSTATEENCRYPTED";
foreach (string elem in aspnet_formelems)
{
//Response.Write("input type=""hidden"" name=""" & abc.ToString & """")
int StartPoint = html.IndexOf("elem.ToString() + "\"");
if (StartPoint >= 0)
{
//does __VIEWSTATE exist?
int EndPoint = html.IndexOf("/>", StartPoint) + 2;
string ViewStateInput = html.Substring(StartPoint, EndPoint - StartPoint);
html = html.Remove(StartPoint, EndPoint - StartPoint);
int FormStart = html.IndexOf("
if (EndForm >= 0)
html = html.Insert(EndForm, ViewStateInput);
}
}
writer.Write(html);
}
to render the hidden viewstate form values to the top of the form so if my page loads slowly these form values get processed first and are not omitted during an event trigger. This didn't work either.
I noticed that these error messages appear when my webpages is idle after twenty minutes. Could this be a timeout issue?
durgaprasad rangulaPosted Apr 27, 2011, 10:59 AM
when the following preconditions are true:
1. You aren't using a web farm.
2. It appears when using built-in databound controls such as GridView, DetailsView or FormView which utilize "DataKeyNames".
3. It appears if you have a large page which loads slowly for any reason.
If following preconditions are true and you click a postbacking control/link and the page hasn't loaded completely in client browser, you might get the "Validation of ViewState MAC failed" exception.
When this happens, if you just try setting the page property "EnableViewStateMac" to false, it does not solve the problem, it just changes the error message in same navigation behavior:
Other exceptions that seem to be the same problem look like:
andRoot Cause
This exception appears because Controls using DataKeyNames require Viewstate to be encrypted. When Viewstate is encrypted (Default mode, Auto, is to encrypt if controls require that, otherwise not), Page adds field just before closing of the