Game always crash when entering Demonis

[Zgredi]

Hello,
mayby someone had this problem and mayby there is solution for that. I'm 26th level Paladin, who just come back form Elves land and now it's time to visit Demonis in order to get a key. No way. Everytime I enter portal in Underground sea game crashs (there is an error and application needs to be closed) or sometimes just quit to windows without any information. Tried one hundred times, always the same. Tried load a bit earlier saves get to the portal - the same.
Please help as I'm completly depressed.