xml is denied

hi, I got the following errors(line 36) when I try " a guestbook.aspx"
will anyone help me?
Thanks in advance..

Server Error in '/' Application.
Access to the path "c:\inetpub\wwwroot\guestbook.xml" is denied.
Source Error:
Line 34: // Insert the new element into the XML tree and save
Line 35: myXmlDocument.DocumentElement.InsertBefore(myXmlElement, myXmlNode);
Line 36: myXmlDocument.Save(Server.MapPath("guestbook.xml"));
Line 37:
Line 38: // Re-bind data since the data has c

Try giving the ASPNET user full control of the folder in which you are trying to save the document. If you're using IIS 6.0, i think its the NETWORK SERVICE you have to give full control.