Do you have a recent save you can reload?
If not, there are a couple ways you can 'cheat' to get out of the prison, and hopefully avoid the crash.
You can use the technique in the topic
FIX for the Missing Catacombs Portal to get out of prison long enough to get a teleporter stone and make sure the other is on the ground somewhere.
I'm not sure if the Polish and English saves are compatible, but you can use a data.000 file from one of your earlier saves, or start a new game if necessary, rather than use my data.000 files listed in the topic.
Or
Get out directly:
Teleporting Anywhere, via hex editor.
If you are trying to get into the potion dealer's back room, Kiya's screenshots
here and
here describe how to do so (save first).
Check your messages (click 'My Stuff' in the top menu bar, then 'My Messages').
