Just after most of the council is killed and Janus speaks to Zandalor again, there is a video played that is on the CD.
Are you using a no-CD hack? If so, the ritual should complete with the CD in the drive. Usually this would bring the game back to the council hall, though, not cause a windows error.
Try running the configuration program and switching to software or Direct Draw mode for the ritual, and maybe reduce the resolution (then save when you get to the wastelands and restore the settings).

Did you see the following in the readme file?

Quote
Problem: The cinematics do not play well. The cinematics are more like a slide show, block or even exit the application.
Cause: the Bink player cannot play the movie optimally
Solution:
1) download and install the latest version of the binkw32.dll: www.radgametools.com
2) download and install the latest drivers of your video card
3) on the ATI Radeon cards, setting the monitor refresh rate to 60 Hz solved the issue:
. a) right click on your desktop, select properties, settings
. b) click the advanced button, and choose monitor
. c) set the refresh frequency to 60 Hz, test and apply
4) if nothing helps, prevent the movies to run by deleting all files *.bik from the Static sub folder in Divine Divinity's install directory. You will not be able to see to cinematics, but you will be able to play the game.

BTW, I have no *.bik files in my Divinity folders.


The ritual is a one-way trip, so any un-finished quests will remain that way (your quest log gets cleared). The save game folders are fairly compressible; a 50MB folder should zip to about 7MB or so.

Did you have any problems with the scrying scenes? This seems like a problem with the video played after the cut scene. Check your CD for damage, etc. One person had some dust on the CD at just the right spot to interfere with the CD-ROM trying to read the video.

Troubleshooting and Manual Install Procedure