exporting to 3ds Max

[easy]

What is the best file type to export a 3d file from Archicad for 3DS Max. I been using the 3ds file type, but all objects seem to be broken up, ie walls don’t join at the corners of a room.

 

This means that any Radiosity solution generated will leave artifacts where two walls meet but not joined. What would you recommend I do to prevent this from happening or will it mean i will have to keep attaching and welding vertices together.