Are you capturing HDV or DV?
If you are capturing DV was it shot in HDV?
What are your settings in FCP.
Your settings in FCP determine what type of video signal FCP looks for. If the camera is not set to send that signal out the firewire connection then, its like the computer is speaking english and the camera is speaking german.
If you are trying to capture HDV and have FCP set for HDV yet have your camera set to send out a DV signal then they are speaking different languages.
Remember the FX1 can play back video shot in HDV as DV footage. So if you are trying to capture HDV but the camera is set to send out a DV signal, they will not communicate.