Hi
I used the walktrough_demo from blender demos as a template for a walktrough, changing all the meshes, leaving the viewer and scripts
in this original file all works fine both in Blender environemnt and after saving runtime
after changes however there are some problems with the floor…
my floor consists off 3 objects now, each has different elevation and shape
1 off the floor objects is a cube, resized only, 2 off them are made after some cuts and extrusions
and now is the problem: when I save to runtime my viewer falls down through the floor at startup if it is placed over one off the 2 modified cubes, when it stands over the simple cube it’s all OK
the funny thing is that when it starts over the simple cube it can walk on the modified ones either, never falling down through any piece off the floor
in the blender window all works fine
In general I’m out off ideas 
Try enabling Game / Show Physics Visualization to see where the object bounds are.
enabling Show Physics Visualisation didn’t show anything at all, will have to get some read on the subject I think
However something has changed after a few tests off different starting locations and trying to add an extra cube below the viewer for startup
now it falls through all the floor… or sometimes it falls into the floor cubes, walking on the bootom surfaces of them…
the only suspicion I have is that is has something to do with the time the runtime takes to initialize itself
after runing the .exe the windows is black for a few seconds and then it’s all over, I am already below the floor falling down and down; the second window says: Dropping physics frames! frames:406 substep 0.0166667 for example