[NaS]

Is the array VehicleModel correctly set up? You use it as index for VehicleNames, so an invalid ID would directly produce an array index out of bounds error. If you aren't sure if that might happen, install crashdetect to see if any errors occur.

Is this the only code in OnPlayerStateChange? If not, make sure it isn't prevented to run by a return or so.

Furthermore your format line isn't really correct. You use %f to show the speed, but the argument is not a float argument. floatround will round a float and return an integer. This will not be correctly shown when using %f for that.
Remove floatround or use %d instead.