I am not using the Rest module, but this error looks very like the errors that you get with the AdvancedGoogleMaps module - referring to JSONObject etc. You can either wait for an updated version of the module, or update the java yourself. You need to search for entries (in the javasource/<module> directory files) like:
and replace them with
I uploaded a new version in App Store. It also addresses some compile errors due to API changes.
'_' Used as identifier can sometimes be solved with project/clean deployment directory