Log.txt
From ModWiki
This is an file used for logging and error reporting by Ableton Live. It's used by the Monomodular Installer on both platforms to determine the locations of several Ableton relative folders so that it knows where to put things.
It can be used for error logging when writing Python Remote Control Scripts. It is best viewed by an application that supports real-time updates of file information (Console.app in MacOSX), so that when errors are logged they are immediately viewable.
OSX /Users/"your username"/Library/Preferences/Ableton/Live 8.x.x/Log.txt
Windows XP/Vista/ C:\Documents and Settings\"your user name"\Application Data\Ableton\Live\Preferences
Windows 7 C:\Users\"your user name"\AppData\Roaming\Ableton\Live 8.x.x\Preferences