With the introduction of NinjaTrader 7, migrating existing NinjaScript files will be one of the first things many users do. As such, providing forward compatibility from NinjaTrader 6.5 was always on the forefront of discussion during the development process and we have maintained compatibility as much as possible. There will be some unavoidable code-breaking changes to several NinjaScript methods and properties as a result of improving the overall product in terms of performance and feature enhancements. In the end, we feel that the changes will benefit all in the long run.
The following thread contains a PDF that outlines the code breaking changes and primarily focuses on supported NinjaScript methods and properties etc... If your product uses non-supported (non-documented) elements we strongly urge you to put your scripts through thorough testing to ensure they still behave as expected.
NinjaScript Code Breaking Changes - Revision 11, October 11, 2010