It would seem that wololo doesn't like hotlinking, I do apologize. The file is definitely up, I've just downloaded it.That link does not work... at all. It just keeps looping me back to wololo's main page. And the mediafire mirror for v4 is down, too.
Try this then: http://wololo.net/downloads/index.php/version/1586 (click the wololo download)
Alternative mirror: http://www.mediafire.com/download/1saa7m6c9js2soc/6.xx Downgrader.zip
Both files download on my end.
EDIT: Just read your update in the previous post... I guess I'm temporarily stumped, I'll have to think a bit about this one. Technically there's no reason why your PSP wouldn't downgrade with the tool you're using.