That rain we just mentioned? It can cause cancellations of the shows and parades found throughout the parks. Additionally, high winds and lightning in the area might cause the fireworks, afternoon parade, or other outdoor entertainment options to be cancelled for the day.
How to fix it: Because this is another weather related issue, you really can't fix or avoid it. If you are visiting the parks for multiple days, you might consider getting a Park Hopper pass so you can return to that park and see the show a different day.