Needs to know meaning of Missing Reference Exception: Object of type 'AfterburnerPhysics' has been destroyed but still trying to access it, your script should check it is null or should not destroy it and how to fix problem.

Hi it's me Richard B. Haley just letting you know that I have this message that says"Missing Reference Exception: The object of type 'AfterburnPhysics' has been destroyed but you are still trying to access it your script should either check it is null or you should not destroy the object", and I was just wondering what does this all mean and how do I fix this problem also too the very right of it, it has the number 58 and I was just wondering as too what the number really means (as well with the numbers with all the other compiler errors and warnings).