query flagged emails in Exchange inbox using XML/WebDav

[gerfla]

I am trying to connect to an Exchange server and return the emails that are unflagged. I have succeeded in connecting to the mailbox/inbox. However when I try adding a where condition (.. i.e. where email is not flagged.) I get no response. In fact I recieve "page not found"
The following code works to return all the emails

        sQuery = "<?xml version='1.0'?>" & _
                 "<g:searchrequest xmlns:g='DAV:'>" & _
                 "<g:sql>SELECT ""DAV:displayname"" " & _
                 "FROM SCOPE('SHALLOW TRAVERSAL OF """ & sUrl & """')" & _
	            "</g:sql>" & _
                 "</g:searchrequest>"

        oXMLHttp.send sQuery

The following does not

        sQuery = "<?xml version='1.0'?>" & _
                 "<g:searchrequest xmlns:g='DAV:'>" & _
                 "<g:sql>SELECT ""DAV:displayname"" " & _
                 "FROM SCOPE('SHALLOW TRAVERSAL OF """ & sUrl & """')" & _
                 "WHERE ""urn:schemas:httpmail:messaggeflag"" = 0" & _
	            "</g:sql>" & _
                 "</g:searchrequest>"

        oXMLHttp.send sQuery

Any ideas?