I am using a custom XMLSiteMapProvider where in i have defined a web.sitemap file with urls.
The application worked fine for administrators but i got this error when i tried other users. I am using this control in a SharePoint 2007 Page . After lots of trial it came to my notice that actual error was not identification of the file .The problem was that the normal sharepoint user didn't had enough permission to access the web.sitemap file in web server .
This worked once i gave autheticated user access to the file,kind of fishy though , as i am not expecting this behaviour.