Same error, uninstalled and tried with a fresh install. First off, it seems to only happen on the Windows 7/8 version of the launcher, it doesn't seem to have anything to do with modded/unmodded since it happens regardless and in my case it also seems that not even the "Keep the launcher open while games are running" option works, both that and the output log close regardless of what settings I have (so it doesn't matter if I have hardware acceleration on/off or if I'm using the beta version of the launcher). Hopefully this helps.
victor6467
Same error, uninstalled and tried with a fresh install. First off, it seems to only happen on the Windows 7/8 version of the launcher, it doesn't seem to have anything to do with modded/unmodded since it happens regardless and in my case it also seems that not even the "Keep the launcher open while games are running" option works, both that and the output log close regardless of what settings I have (so it doesn't matter if I have hardware acceleration on/off or if I'm using the beta version of the launcher). Hopefully this helps.