Hi, ddkd726,
It appears that there may be corruption in the movie at around the 50% point. Expand out your timeline and slowly scroll through your time line at the 40% thru 60% range. Look for black frames, white flashes, artifacts and any other signs of corruption. Cut out any that you find and try to reshare. Work with a duplicate of your project so as to preserve the original.
Again working with the duplicate, you can try deleting the second half of the movie and then sharing out the first half. See if you get a good export. Then create another duplicate of your original project and delete the first half, then sharing out the second half. You can keep deleting sections and sharing out the remainder until you narrow down where the corruption is.
Also, to rule out a corrupt preference, try deleting preferences. To delete preferences open iMovie while holding down the Option and Command keys and select to delete preferences in the box that appears. iMovie will open in a new library. Reopen your old library to get back to your projects. Now see if you can get a complete share out. Deleting preferences is a safe procedure that will not cause data loss or disruption to your project.
-- Rich