When trying to publish an Mp4 in Captivate 8, I get to about 90% then I get an APPCRASH error and it shuts down. Does anyone know why or if there is any way around it?

A lot of things can cause this...

Do you have enough RAM available? Try restarting your computer, just launch CP and nothing else, load the project, and publish.

Do you have enough HD space available? Be sure to free up as much HD space as you can.

Could be something funky in you project. If none of the above help, make a copy of your project and delete half the slides, then publish. Does it work? If so, something in the deleted slides is causing a problem.

If that doesn't work, create another copy and delete the other half of the slides, then publish.

Vary that effort until you get a complete publish and can hopefully narrow down where the problematic slide is.

Otherwise, you can try different MP4/audio settings and see if that makes a difference.