Google direction api request invalid in ios5
===

Here is my request:
https://maps.googleapis.com/maps/api/directions/json?origin=49.276951,-123.128559&destination=49.277874,-122.912404&mode=transit&sensor=false
The result is:
{
   "routes" : [],
   "status" : "INVALID_REQUEST"
}

It worked before, but it does not work when i used it today. why is that?
Note: it works fine when i change it to mode=walking 
