Star Trek Convention Fiasco
In 1976, the giant Star Trek conventions seemed to hit a wall: The Chicago Star Trek/Space Spectacular, "The Greatest Show Since Earth" was held in June. The committee did heavy advertising including TV spots, and had rented the Chicago Amphitheater, which seats 13,000. The got 200 people on Friday and 800 on Saturday and then cancelled the convention. They did not pay the stars who came and the convention was reported to have lost multiple hundreds of thousands of dollars.
Other Star Trek conventions that failed in 1976 included the Boston Star Trek convention in April, a Tampa convention in June, and a Toledo Star Trek convention. The Toronto Star Trek convention lost money and the New York Star Trek Roast was cancelled "for lack of interest".
Almost as bad, the convention held at the New York Hilton on January 23-25, 1976 attracted an crowd estimated by the New York Times to be between 20,000 and 50,000 people and completely swamped the hotel. This did not bode well for the giant SF Expo to be held there in June. See Star Trek Lives! for more.