Sulbanyer told you that the poison was completely new to him. The only hope of an antidote was examining its source directly. Searching Udas Temple for the source, you discovered the Toxic Caverns. There you found Kingspin, a huge Arachna that was obviously the poison source. You exterminated Kingspin and returned to Sulbanyer. He promised to make an antidote from Kingspin's remains, and thanked you for your assistance.