gta vice city help

i installed gta vice city game and played well but yesterday i installed back to the future hill valley gta vice city mod, in gta vice directory its runs. when i start new game it start from starfish island where i have to pick delorean and then goto garrage for convert to time machine and then pick plutonium to refuel it then travel in time and back to garage after that car convert to helicopter and have to come back to star fish island . this is done without problem. but after leaving helicopter it changes to car back and gates of island closed on both sides. before picking delorean from starfish island all gates are open but after time travel every gates closed and clue appear for clear task. anyone have any idea . plz help how to play