For example a GridView didn't show inserted or updated data unless we refresh the page (F5). Or if we restart IIS (iisreset).
After some googling it was apparent that this is an IIS6 issue.
And every try to solve it by setting caching and expiration settings in IIS 6 failed.
The only solution we found working is to hardcode the following in Global.asax
protected void Application_EndRequest(Object sender, EventArgs e)
{
HttpContext.Current.Response.CacheControl = "no-cache";
}