Do you mean the Lakes at Fen Drayton?
As I understand it, there are issues/faults with the route that make it unusable for buses. As has already been said, the Council and builders are in dispute as to who pays for the work to correct things. At the moment it's the most expensive Cycle/Dog Walking Path in the UK!
The thing is, nobody wanted the guided bus route in the first place. Even the guy who designed the system said it wasn't suitable for the job!
What really annoys me is that the people that agreed to this, despite all the objections, are long gone and wont be held accountable!