"illegal" RDF generated by PutData command

When PutData (http://rhm.cdepot.net/bin/PutData)
generates/edits an RDF file, it uses this RDF header.

<rdf:RDF
    xmlns:tkb=""
    xmlns:dc="http://purl.org/dc/elements/1.1/"
    xmlns:a="http://tap.stanford.edu/2002/05/GetDataSchema#"
    xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
    xmlns:daml="http://www.daml.org/2001/03/daml+oil#"
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
    xmlns:tap="http://tap.stanford.edu/data/">
 
When I try to read the RDF file with MS Internet Explorer 6, I get this error

The XML page cannot be displayed 
Cannot view XML input using XSL style sheet.
Please correct the error and then click the Refresh button,
or try again later. 
--------------------------------------------------------------------------------
Only a default namespace can have an empty URI.
Error processing resource
'file:///C:/Documents and Settings/All Users/Documents/tap/kb/MacPherson.rdf'.
Line 12, Position 47 
    xmlns:tap="http://tap.stanford.edu/data/">

I can work around the problem by replacing 
    xmlns:tkb=""
by
    xmlns=""

My questions are
1. what is the significance of "tkb"?
2. should TAP be changed to avoid this error?
============ 
Dick McCullough 
knowledge := man do identify od existent done;
knowledge haspart proposition list;