It's likely that the clip has become corrupted. This can occur if the camera is shut off or loses power while still trying to record. Or, the memory card has gone bad.
Sometimes the camera can try to repair the file, but it sounds like it cannot in this case. About the only thing I can recommend is copy the file to your computer and see if any parts of the file is salvagable. If it was really crucial footage, could also look at data recovery services.
--
Ricky
Camera: EOS 5D IV, EF 50mm f/1.2L, EF 135mm f/2L
Lighting: Profoto Lights & Modifiers
