I've got exactly the same problem since quite some time now (and maybe it's indeed caused by my firewall, which automatically updates).
However all builds except the very last "nightly build" (=500) can be found at another (download)site, which gives no problems whatsoever.
Please refer to my earlier post on this ....:
http://forum.bsplayer.org/viewtopic.php?p=5204#5204
or go directly to that particular download site:
http://www.dvd.box.sk/index.php?pid=...=info&rid=7499