First off I have no clue why you're using some obscure outdated racing game when there are many great free alternatives out there, plenty of which are flash/java based.
When it refers to "JIT debugging" it's talking about what's called a "just in time" compiler-- in other words, the source code is compiled just as it's about to run. The program is essentially telling you that you need to change around the options in the game, and presumably there is some sort of options menu that allows you to do this. Otherwise, you'll have to go ahead and browse through the code and change it yourself.
Or you could go on addictinggames.com or miniclip.com or any of the hundreds of other game sites and find another game. Just saying.