Can't Compete in Equestrian Competition

[Mack Whitman]

When I try to have my horse compete in any of completions (racing, jumping, cross-country) the competition never starts.  I go during the times that the competition is on and both horse and rider walk in but they don't compete.  I've left the characters in there over a fully Sims day and they just stayed inside.  The only way out was to reset the sims.