I'M EXTREMELY MAD AT THIS!!!
Dude calm down i know what you feel i have worked on something for a while and then i save then came back and ran it and it worked then did something like add breakable lines and then POOF it stopped working in the beginning
i will always hate that thing that caused it. LOL well its behind me.. its ok just make a track again and try to replay it every now and then to double check it.. Trust me it helped me a lot.. Because one of the problems with my track was a new line that messed up his balance and messed the whole thing up because i made the track to close together in a tight space LOL.. I will never forget it.. 
I was working on a track and when I was done with the track naked, I decided to put in some scenery.(I played the whole track from start to finish) I did some scenery at the beginning, and then played it to see how it looked. FOR NO REASON IN A PLACE JUST PAST THE SCENERY HE CRASHES AND THE WHOLE TRACK WAS THROWN OFF!!!! I only used scenery lines so I have no idea why the physics of the track changed so randomly and since that was the beginning of the track, all of my work was wasted!!!!!
WHAT HAPPENED!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
(and why)
(and you'd better make a patch for this!!!)
If you have sisters more annoying than Elmo's voice, then put this on your sig.