It's an error..... errors aren't normally talking to the user, they are talking to the person who can do something about it.
Now that we know what the error is (THANK YOU for actually telling us what it was, mucho kudo for that
) here are some other things we need to know in order to help you:
1) Are you using a Mod of some sort?
1a) If yes: Which Mod? Which version of FPSC did you install it on?
1b) If no: What version of FPSC do you have?
2) Have you tried making a super simple level? (A level that consists of a small room and the player and nothing else)
The one and only,