9-patch image error in Android

Whenever I try to add a 9-patch image to the \drawable folder in my project, I get the same error:

ERROR: 9-patch image C:\...\res\drawable\appwidget.9.png malformed.
Frame pixels must be either solid or transparent (not intermediate alphas).
Found at pixel #3 along top edge. Failure processing PNG image
C:\...\res\drawable\appwidget.9.png

The weird thing in this example is that I've got this image from the "android-g1-icon" images found in the SDK resources, so it is supposed to be OK. The same happened with any 9-patch image I've tried so far. What could be wrong?

I have encountered with same problem on Android Studio:

AAPT out(943142208) : No Delegate set : lost message:Done
AAPT err(943142208): ERROR: 9-patch image /Users/cartman/Github/UteacherAndroid/RefactorDemo/app/src/main/res/drawable-xxhdpi/nav_shabow.9.png malformed.
AAPT err(943142208):        Frame pixels must be either solid or transparent (not intermediate alphas).
AAPT err(943142208):        Found at pixel #1 along left edge.

This is how I resolved it: Open draw9patch tool under your Android Sdk directory

cd /Android/sdk/tools
./draw9patch

Open .9 png and save it again. Hope it helps.

This is the problem with the latest ADT that is 20.0.3. You can instead rename the *.9.png to *.png and start working.

I think this is the bug with the ADT only, since for 18.0.0 version ADT it doesn't prompt for this type of error and works fine.