I'd definitely suggest patching the game.
You can find the last official patch (which includes Trials of the Luremaster)
here.
Note, you need to have Heart of Winter Installed for this particular patch/expansion.
You can find the patch for the vanilla IWD (without HoW installed)
on this page.
Other than that, I have no idea what it could be, especially since your man is not having the same problems. Maybe you somehow have a corrupted save???