Why blender splits my imported model in pieces? I created a model in Sketch-Up (Sketch-Up detects it as a solid, a closed hull, where all faces can be seen from outside).
Then i exported it as Collada  .dae.
But Blender splits 5 faces off and converts them into separate objects, each one out of two faces, one face lies flat on the other one.

This is the link to the original-sketchup-object

This is the model in Blender. Main part moved to set the separated objects : 



Why does this happen?
Well its pretty unusual workflow, so dont aspect everything to work.
however maybe blender can save your day
make sure to join all loose objects  (border select on screen and join them).

Next in edit mode try verticles remove doubles.. if your lucky itss all connected afterwards
next recalculate normals.