No key.store and key.alias properties found in build.properties
I had this problem too recently, I think that that tutorial is out of date...
The key.alias etc directives need to be in a file named ant.properties. There's no file called build.properties any more.
Ultimate answer of any this kind of question is in android-sdk/tools/ant/build.xml
Document is at http://developer.android.com/guide/developing/building/building-cmdline.html
regarding 'Sheehan Alam' issue that follows file name fix
[signjar] jarsigner error: java.lang.RuntimeException: keystore load: ...
You probably have key.store set to a value with a full path.
Make sure that you are using '/' and not '\'.