Thank you Raze.
Finally got the grail after several tries (it's the problem I described in my first post when clicking/dragging an item into my inventory).
A new problem, once I get the grail the main boss and all the guardians attack me as you said. After several fruitless attempts to fight them all, all ending disastrously, finally ran for the exit and they didn't pursue.
Snag is I can't access the tunnel to the right as it appears to be blocked. I must confess I can't remember how I got into the antechamber with the glowing door. How do I escape? I'm level 27 by the way.
