Maybe one of your add-on widgets downloaded from the App store uses `_ValidationHelper`?
`_ValidationHelper`was never public and hence not available in Mx 7.0.
Arjan was correct. The widget "SetFocusOnErrorWidget" is no longer supported. I removed references to it in my applicaiton and everything is working great.
Overall, the upgrade to 7.x required that I remove some APM jar files, update all my app store modules, and test my widgets for compatibility. To test the widgets I ran the Tools-Test Widget menu option. This told me that the SetFocusOnErrorWidget would not work.