java.io.IOException: Target platform: "null" not found.
Make sure that "build.target" in the
preferences file points to a subdirectory of
/Applications/DevelopmentApps/arduino-0012/hardware/cores
... long string of java errors
There seems to be no "build.target" in my preferences file. I also tried deleting the old prefs file and restarting Arduino to insure that it built a new one.
The boards.txt file is (currently) stored with the Arduino application, so changes aren't automatically carried over between versions. If you've modified your boards.txt file to include new boards and selected one of them, you'll get that error when you try to run a different version of Arduino. I'll probably move the boards.txt file to your home directory at some point, but I wanted to take a few versions to let its format stabilize first.