The file web.sitemap required by XmlSiteMapProvider does not exist

Hi There,
    When I open my asp.net website with a browser, I get the following error:

The file web.sitemap required by XmlSiteMapProvider does not exist

even though the web.sitemap file is where it's supposed to be in the root folder.  I can't figure out why it's giving me this error.

I'm trying to create a tree view navigation control on the homepage.  I created the web.sitemap file, added the sitemap datasource and added the navigation control and pointed it to the datasource, but when I navigate to the page I get that error.

The site root folder is located on a test webserver in my office running IIS.  I create the files on one computer, and save the files to the root of the webserver folder which is shared. Not sure if that has anything to do with it.

Thanks for any help!