If I remember correctly, there is a 'feature' of the Crimson XML parser
which means it treats the BOM (byte order mark) at the start of UTF-16
encoded file as text, and so throws an error when it encounters your
opening <xsl:stylesheet> element. This is compounded by the fact that
Notepad inserts a BOM even if you save the file as UTF-8 (not sure why,
or what use it would be).

It's possible then that you are using Notepad and saving your file as
either UTF-8/UTF-16, and then using Crimson to parse it. The fix is to
use Xerces instead of Crimson (and you should never use Notepad ;)