I used two free night at a Holiday Inn property last year and, despite having emails showing that the free night should not have attracted any fees was charged them. The hotel wouldn't budge, IHG customer care were not interested and as I had used an IHG credit card they advised they wouldn't raise a dispute against an IHG property as it was "biting the hand that feeds them".
IHG are deliberately misleading customers here. I would only use the free night at a property with no resort fees. I also transferred 90% of my business away from IHG to Hilton and I can say it's an altogether much more pleasant experience.