You can hack the 'sencha' shell script to see the error that's occuring. By default, it seems to output stderr to a file called 'stderr.txt', but then deletes it before the program exits. So if there's an exception, you just get blank output.
MAKE A BACKUP COPY ?of the sencha command first.
Look for this line:
Remove the redirection of stderr to stderr.txt, so the line now reads:
java $jvmArgs -jar $BASEDIR/sencha.jar "$@" 2>stderr.txt
Now, if there is a Java exception, you'll see the stack trace on the console so you have an idea of what's wrong.
java $jvmArgs -jar $BASEDIR/sencha.jar "$@"