In my case, I update as an SDK component. I tried to set-up a new project after updated, the error of ".../tools/lib/proguard.cfg (No such file or directory)" reported. proguard.cfg file is automatically generated when you create an Android project(http://developer.android.com/guide/developing/tools/proguard.html).
I compare the content of my existing Android SDK folder after updated, and that of a fresh new downloaded Android SDK, the file /tools/lib/proguard.cfg is missing in my case; may be that's why I can't generate proguard.cfg accordingly. So I re-setup my Eclipse to use the fresh new SDK, the problem have been solved. As it should be, I have to re-setup the Android SDK location and AVD.
