the same thing happens to me, when it happens turn off your computer for 1 minute and turn back on then start the launcher before starting anything else
Launcher Version: 246
Operating System: Mac OS X 10.8.3
Java Version: Java 7
Antivirus Program: none
Description of Problem:
when ever i launch a mod pack they open a window ,the screen is white ten goes black then closes
Error Messages:
Error Log: