Ableton just released the latest bug fix update Live 4.0.4. To get this version please go to the download section of their website: www.ableton.com/downloads or use the “Check for Updates” function within Live’s help menu.
You DO NOT need to uninstall a previous Live version to install Live 4.0.4. You can install the new version in parallel. Rather the opposite Ableton recommends to keep the existing Live version until you have checked out Live 4.0.4.
Ableton has made 32 improvements and bugfixes with the 4.0.4. version of Live. A complete list can be read at http://www.ableton.com/forum/viewtopic.php?t=13271