build/core/java.mk:20: *** dalvik/dexgen: Invalid LOCAL_SDK_VERSION '4' Choices are: current . S

解决：

first try: "rm -rf prebuilt ; repo sync -l prebuilt"

If that's still not enough: "rm -rf prebuilt ; repo sync prebuilt"

If that's still not enough and you have a solid internet connection:

"rm -rf prebuilt .repo/projects/prebuilt.git ; repo sync prebuilt".