When you install Logic Pro X on a Mac with an already installed Logic Pro v8 it might happen that Logic Pro v8 won’t start up anymore or it will crash during startup.
Solution:
go to –> /Users/YOURUSERNAME/Library/Preferences
and delete the following files that set the logic pro v8 preferences:
com.apple.logic.pro.cs
com.apple.logic.pro.LSSharedFileList.plist
com.apple.logic.pro.plist
when you start up both programs the .cs file sould not appear anymore. now you can use your old logic pro v8 projects with all of your 32bit plugins and your of course for your new projects logic pro X!