I just fought this today (23 May 00) and he conned even to me at lvl 46. The above posts are definitely correct. It resist all roots/stuns and lightining based spells. I did however get partials and fulls on fire based using conflagration. Make sure not to taunt, it's a nasty spider for a caster to engage.
Stuns and root never work on it. I am a 49 wizard and I have yet to see one stick.
Conflag though fire-based hit for full or partial a lot. Now that Rend is saving properly vs magic instead of cold, I suspect it won't be effective against it anymore. IC hits but is partial too often for me, plus the taunt will definitely get you killed.
Caster chip away cautiously not to aggro, and let 2-3 tanks do the work. And have a good healer or two there.
After several hours fighting in the "stone room" this is my advice..
try to have poison/disease Dot casters in the group. I had 1 dot resisted out of 8 on the stone spider..its resistances for dis/poi are normal, all magical attacks are futile, save the mana, they will hit very very rarely.
I think that you have the loor reversed. The BCP seems to be his "more" common loot. I was camping him this past weekend fr=or the exp and he dropped 9 BCPs and just one orb.
These actually aren't very rare at all anymore. Practically everyone has one, or is selling one, as to every time I go into EC there is more than one person selling it. On Quellious server the price has dropped from 1k to about 600-700pp I've even seen it sold for 450pp which is very cheap! Possibly the price went down cause it's common now or cause Velious rigged everything with it's phat loot. BTW what server sells the thing for 2k+? That's nuts!