IE hangs with an external DTD

I've got an xml document and dtd. If I include the DTD as an internal the xml displays fine in IE and I've put it through a couple of validators on the web which report no errors. But when I put the dtd into an external file (quite important for this project) IE just hangs. It doesn't report any errors but I can't seem to collapse any of the nodes which (I think) means the xml is invalid. Could anyone suggest why this would be?

the reference to the dtd reads:-
<?xml version="1.0" encoding="ISO-8859-1" standalone="no"?>
<!DOCTYPE EnhancedSupportReport SYSTEM "C:\TMP\EnhancedSupportReport.dtd">

and the dtd itself reads:-
<!ELEMENT EnhancedSupportReport (company, queries)>
<!ELEMENT company (#PCDATA)>
<!ELEMENT queries (query*)>
<!ELEMENT query (no, name, results)>
<!ELEMENT no (#PCDATA)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT results (row*)>
<!ELEMENT row (field, value)*>
<!ELEMENT field (#PCDATA)>
<!ELEMENT value (#PCDATA)>


I know it finds the dtd because if I add some garbage to it I get apropriate error messages so I guess something's wrong in the DTD but I can't see what.