strange error- "Document root element is missing"

Hi,

I hope someone can shed light on this. I'm parsing an XML document that 
I've validated- it is well formed, and I'm getting this error: 
'org.xml.sax.SAXParseException: Document root element is missing'

The xml is thus (I've stripped out everything but the root element, but 
the error is the same):

<?xml version="1.0" encoding="ISO-8859-1"?>
<alert>   
</alert>

I've read postings on problems with a byte order mark being inserted at 
the beginning of the file, but I've opened up the document in a couple 
of Unicode editors, and can't see anything there, and there's no 
whitespace before the xml declaration.

Any ideas or advice greatly appreciated.

Thanks

Alan Eustace