Treeview Problem "There is invalid data at the root level"

[Ulli]

I am trying to use the TreeView Control that is part of the WebControl
package from Microsoft

Iam getting this error
Exception Details: System.Xml.XmlException: The data at the
root level is invalid. Line 1, position 1

The error ocurrs only if I uncheck the "Anonymous Access" in the IIS. (But I need to uncheck, because I want to read the Username of the authentificated user
Otherwise the treeview works fine

Any help would be appreciated

Ulli