If I understood correctly, i'm assuming you have the Physics Behavior enabled on your character and the ground. If your floor and character is falling then you need to turn "Immovable" on in the Physics -> "Behaviors" panel on the (Default) left side, for your ground only.
Hopefully that helps.
Edit: Forgot! You can use the Platformer Behavior for your character and just add the Solid Behavior to your ground, and you should be ok.