I shoot with 50 frames per second option, and when I playback it in the camera it is a slow motion, but I can not import it in final cut. When I do the import p2 and then select the clip and press import, if it is in a higher frame rate it shows some error.

What could be the reason?

You must first set the framerate to 25p, then set the recording rate (in the scene file) to 50, and you'll be fine.

Gunleik