I have the same issue when generating jsb file
opt/SenchaSDKTools-2.0.0-beta3/sencha create jsb -v -a index.html -p app.jsb3. However, when accessing index.html over http
/opt/SenchaSDKTools-2.0.0-beta3/sencha create jsb -v -a http://localhost/js/index.html -p app.jsb3 it works.