Parsing XML

I am using VB6 and MSXML to parse an XML file. It was working happily for over a year. Now when ran I get:

The download of the specified resource has failed.
Error Processing Resource

This was the code:

' Loads XML file into memory and parses out pertinent information
objXML.async = False
result = objXML.Load(lblInputFile.Caption)

If I add objXML.setProperty "ServerHTTPRequest", True before loading the XML file it works.

Could someone please explain why?

Thanks.

Swi