What does "three tracks with bundles are needed to orient the floor" mean? I have selected few tracks on the floor (three or more) and press the Floor button. As a result I get the following message:


  Three tracks with bundles are needed to orient the floor


What does it mean? What is "with bundles"? What are "bundles"?

UPDATE

Below is an example. Five tracks are selected, all of them are of same color. How can I see that some of them has no "bundles"? I was pressing "Solve Camera..." button before.
In order to create the floor you have to solve the clip first. bundles are basically solve data for the track. Your error is probably caused by unsolved/incorrectly solved tracks.

From the wiki:


  Bundles makes sense after solving the movie clip, and it works in the following way: the solved position of each track gets projected
  back to the movie clip and displayed as a small point. The color of
  the point depends on the distance between the projected coordinate and
  the original coordinate: if they are close enough, the point is green,
  otherwise it'll be red. This helps to find tracks which weren't solved
  nicely and need to be tweaked.