Nick - Check out this KB article on caching issues with the MXSML Parser: 
887606.

BTW - I too have a major problem with IE6 not loading an XSD file since I 
ran SP2 for WinXP. IE6 will load XML and XSL files, but not an XSD. Wassup 
widdat?

"Nick" wrote:

> We develop and host a webbased accounting application which is fully xml/xsd 
> and webservice oriented.
> 
> We have recently noticed that xml schemas (xsd or xdr) are not being cached 
> by Internet Explorer, or at least the cache isn't being used anymore. We know 
> for a fact that this was working properly until recently: if-modified-since 
> headers would be sent to the server which then replied with 304's, but now we 
> see that these headers are not being sent anymore, forcing the server to 
> respond with a 200. We suspect it must be due to some recent windows update 
> (urlmon, wininet, msxml ??) but we're not exactly sure when.
> 
> When the schema is directly requested through the location bar of IE it is 
> cached correctly while if the xml parser is allowed to resolve it as an 
> external the cache is by-passed (no if-modified-since header).
> 
> Our XSD is over 140kB and caching is obviously crucial to the performance of 
> our application.
> 
> Any comments, suggestions, similar experiences?
> 
> 
> Thanks in advance
> 
> 
> 
> 
> --------Sample XML-file:---------------
> <?xml version="1.0" encoding="utf-8" ?>
> <DATA xmlns="x-schema:schema.xsd">
> 	<CUS>
> 		<CUSNBR>1</CUSNBR>
> 	</CUS>
> </DATA>
> 
> 
> 
> --------Sample XSD-file:--------------
> <Schema xmlns="urn:schemas-microsoft-com:xml-data" 
>         xmlns:dt="urn:schemas-microsoft-com:datatypes">
> 	<ElementType name="DATA" content="eltOnly" order="many">
> 		<element type="CUS" maxOccurs="1" />
> 	</ElementType>
> 	<ElementType name="CUS" content="eltOnly" order="many">
> 		<element type="CUSNBR" maxOccurs="1" />
> 	</ElementType>
> 	<ElementType name="CUSNBR" content="textOnly" dt:type="int"/>
> </Schema>
> 
>