Which version of the program are you using and on what operating system?
Have you ensured you have the latest version of Quicktime from Apple?
Please describe the steps you're taking to output your video and what you're seeing when you do each.
I am using adobe premiere elements 11 on a mac osx version 10.9.2. I am
using the lastest version of Quicktime. I am going to the publish and share
tab in the upper left hand corner. Then I go to Computer: view files for
viewing on computers. When I select this option the presets and settings
tab comes up, then I click save. Then a screen will pop up saying my video
is being rendering and saved. Then a message comes up that says 'error
compiling video:unknown error'
Are you able to output your video using Publish & Share/Computer/AVCHD with the YouTube SD preset?