lost path

I've got an elevator with two path_track entities,and a func_tracktrain. All the models and player clip brushes are parented by the func_tracktrain. The elevator works alright after the second round, but on the first round, it outputs the following when you press the button.

input : lowerElevButton.Use()
output: (func_button,lowerElevButton) -> (elevCompare,Test)
input lowerElevButton: elevCompare.Test()
output: (logic_branch,elevCompare) -> (lowerElevButton,FireUser1,1.5)
input elevCompare: lowerElevButton.FireUser1()
output: (func_button,lowerElevButton) -> (elevator01,StartForward)
input lowerElevButton: elevator01.StartForward()
TRAIN(elevator01): Lost path
TRAIN(elevator01), speed to 0.00

any ideas?