Another way to accomplish the provided error is to use the "Reset" button under the "Debug" menu item. Do not press this button as it will erase all of your memory objects and the only way to bring it all back as far as I know is to restart Illustrator.
Even if you had never pressed this button, I suspect the issue is caused by the same reason: your "Data Browser" panel in the ESTK appears to be empty of all variables. Usually you should see a long list of constantly-existing necessary global variables in this panel, among which is the pre-defined 'app' variable.