I had the same problem " Error 404 on downloading iCal"
on the same version "3.6.4 Stable".
Used the same fix "Please unzip and upload this file to components/com_jevents/router.php it should resolve this issue."
and got the same result "404 Unknown Task"
BUT my installation do not "seems to work", ever after waiting 30 min.
Sorry.

What to do?