Sorry you are having this problem. The cocoa error is a general error so doesn't give us much info to go on, however if you can do a Project Archive for us we will take a look at your project and figure out what the problem is. I will send you information on how to get a project to us. Look for a mail from email@example.com
Historically there have been some clips that iOS will play, but it doesn't like the first frame of the clip to be exported from a timeline. So one thing to check is whether there are any clips you have used the very first frame of. If you have, double tap to use the slip trimmer to eliminate the first frame, or trim in another way.
Also, if Dave's suggestion and the one above doesn't work you could try to find the problem like this:
Make a duplicate of your project and then delete the second half and try to export it
Do the same again but delete the first half and try to export it.
Does one half work and the other half not work? If you continue a couple more times you may be able to narrow this down to a certain clip that is causing problems. It may also be the clip at the timecode of the problem, so check carefully at that area.