hello.
well, unfortunatelt, this seems to be an internal error which is very difficult to debug, i've found where the problem, but i still haven't understood why the code was written like that. the problem lies in the renderformcallback method of the pagerequestmanager class.
here's the code that is responsible:
if (this._owner.IPage.EnableEventValidation)
{
HtmlTextWriter writer2 = new HtmlTextWriter(TextWriter.Null);
foreach (Control control1 in containerControl.Controls)
{
control1.RenderControl(writer2);
}
}
rendering the control is necessary for the watermark extender to add the necessary scripts into the page (they'll ony be added if the render method of the scriptmanager control renders itself, ie, if its render method is called and this will only happen when EnableEventValidation is true as you can see from the previous code).
since this is a private auxiliary class used by scriptmanager, there's not much that can be done for now...