"failed to launch fatal error occurred (4)" and then shows a missing directory for the minecraft.jar file.

When logging on to Minecraft on our Mac we get an error that says "failed to launch fatal error occurred (4) and then shows a directory for the minecraft.jar file. Our problem is that the directory with this file only shows if Minecraft is open and we can't open it due to this failure. We chose "not now" but that showed "done loading" with the bar stopped indicating not loaded. We also tried force update but that didn't work. We are using OSX 10.8.2. Any ideas to help my son and I? Thanks