based on your description, i'm inclined to think that the intent of the organizers was probably something along the lines of country club casual. a day dress that's not overly short or low-cut would be appropriate, as would a blouse paired with a skirt or slacks.
avoid t-shirts, sweatshirts, any type of loungewear, flip-flops, and shorts. very dark, dressy-looking denim (i.e. no distressing or loud contrast stitching) may be suitable depending on the specific function, but it's probably safest to avoid denim altogether.