Changes in groovy.json.JsonOutput require extensive permissions that aren't compatible with some web frameworks.

It seems beginning somewhere after 2.0.1 but most likely in 2.0.5 there were some changes in groovy.json.JsonOutput that make it use certain methods or libraries that are restricted in App Engine. Perhaps it was made multi-threaded?

If Groovy is going to support App Engine, these changes will have to be rolled back or made more configurable by allowing the developer to specify wether they want to leverage multithreading or not (If multithreading is the issue).

https://github.com/glaforge/gaelyk/issues/167