I have found an sealed door with a glyph in front of it in the Castle passage between the Drow Catacombs and Castle Cormanthor. Behind this door has to be a demon. But I could not open the seal. in my quest logs it says I have unsealed the glyph of the moon and have to defeat the demon but I cannot reach him. I have pleayed through all the game right now. and this is the only quest I need to do that is left.
PLease help