Checkpoint editing guide
First you gotta know that leadfoot uses a system called lap tracking (checkpoints) wich is contained in a file with the extension (.lt)
If you get black flags on a track you've edited, then most likely your problem resides in this file.
The LT file explained
Open up a .LT file with a text editor like notepad.
The first number in the file is the number of checkpoints.
The one next to it I think it tells the game wich terrain to use (0 = the 1st terrain,
1 = the 2nd). Yes you read me right, in the DE2 there is 2 terrain.
All the following lines are checkpoints.
X value, 0.000003*, Z value, width of the checkpoint **
* This value must be set to something very close to 0 but not 0
** to know the correct x,z values you will have to open the track in the DE2 editor and check the vertex of the track. The 0,0,0 is the center of the universe in the DE2 editor.