Same happened to me a few weeks ago but seems to have resolved on its own. Make sure the cavities are clear from things (crumbs, etc) and make sure locking mechanism springs back on dock (without the tablet first).. Then try and combine both and push tablet in firmly for a good tight secure fit.
There are two indicators to know if your tablet is in all the way.. The first you know, the little release latch on the dock needs to be in lock position, and the second indication is when you fold the dock and tablet shut, the tablet's edges need to align to the dock's edges.
Hope that helps some.
Sent from my ADR6400L using Android Central Forums