final cut express - tried to capture some frames, but it just wouldent work

Hey i just recently got final cut express... I tried to capture some frames, but it just wouldent work. The video showed up and when i clicked capture now it has a little window that says soemthing like the frames were unable to be recorded :s i dont know how to fix this. When i connect my cam and firewire up with i movie it works perfectly :s