Final Cut Pro allows you to make a number of settings that control different aspects of its behavior while capturing media. One of these settings is "Abort capture on dropped frames" (Final Cut Pro > User Preferences > General).
With this option selected, capture stops immediately when a dropped frame is detected. When capturing to a directly connected or internal HFS+ volume, all media for the clip that was captured up to the point of the dropped frame is preserved. A clip for that media file is placed in the Browser.
But if you're capturing media to an Xsan volume, the "Abort capture on dropped frames" setting behaves differently: The clip media up to the point of the dropped frame is not preserved.
If this occurs, you can try to capture the clip again. If the cause for the dropped frame is not due to a problem on the tape, the next capture attempt may proceed without issue. But if repeated attempts always result in an aborted capture, you can re-log the clip, setting its outpoint to just before the point where the dropped frame occurs. This should allow you to capture media up to that point without difficulty