http://www.spaceflightnow.com/news/n1012/08akatsuki/

"We have found that the orbiter was not injected into the planned orbit
as a result of orbit estimation,"

In other words: we didn't get the maths right and fired the thrusters
at the wrong time...

This is simply embarrasing! Why didn't they ask NASA or ESA to verify
their calculations? Now they'll have to wait six more years for another
attempt and it's unlikely the craft will still be functioning then.