Hi there, did you check that the Landscape has navigation thing on (Sorry I can´t check the right name of it, im on Work now xD)? There should be a boolean (a box which you can check or uncheck) for Navigation.
The other thing what I remember is, that eventually the BlockAll blocks also the nav mesh. Dynamic Generation works only when the game is started. Before it is disabled. So this could also be a missunderstanding?!