title: Unexpected exception thrown when looking up user information
body: <p>I have some code that is looking up group memberships from local groups on a machine. For each member, it tries to load some information about the user (eg. find a group and get the names of each of its members).</p>
  
  <p>The code:</p>
  
  <pre><code>using (DirectoryEntry machine = new DirectoryEntry("WinNT://" + Environment.MachineName + ", Computer"))
  {
      using (DirectoryEntry group = machine.Children.Find(groupName, "group"))
      {
          object members = group.Invoke("members", null);
  
          foreach (object groupMember in (IEnumerable) members)
          {
              using (DirectoryEntry member = new DirectoryEntry(groupMember))
              {
                  member.RefreshCache();
                  string name = member.Name;
                  // &lt;code snipped&gt;
              }
          }
      }
  }
  </code></pre>
  
  <p>The code works fine most of the time, but for some group members, it throws a <code>FileNotFoundException</code> when the <code>RefreshCache()</code> method is thrown:</p>
  
  <pre><code>System.IO.FileNotFoundException: 
      The filename, directory name, or volume label syntax is incorrect.
      (Exception from HRESULT: 0x8007007B)
  at System.DirectoryServices.Interop.UnsafeNativeMethods.IAds.GetInfo()
  at System.DirectoryServices.DirectoryEntry.RefreshCache()
  at GroupLookup.GetLocalGroupMembership(String groupName)
  </code></pre>
  
  <p>What is causing the <code>FileNotFoundException</code> (and what file is it looking for)?</p>