A Mysterious Error

[Mourdret]

H'lo, I'm having a problem. I recently had to reinstall Icewind Dale and start playing it from the beginning. The game works fine until my two rangers advance from level 2 to level 3. After distributing their weapon proficiency point, I click on 'accept', and the game quits, taking me to desktop and leaving this error message:

"An assertation failed in Objcreature.cpp at line number 15689"

I have tried reinstalling and starting the game over, advancing in different area screens, advancing in a different character order, removing equipment and advancing, etc. I run Windows ME at 'regular' installation size. I have tried the game with the 1.06 patch installed and without. I have also tried searching for the file 'Objcreature.cpp' so I could perhaps replace it manually from the CD, but I haven't been able to find it. Can anyone help?

Thank you for your time!