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