TypeError: Error #1009: Cannot access a property or method of a null object referenc

[thedark_master]

It appears when I click the Next button on the window with the likert scale. I have no idea why its giving this error. Please help

TypeError: Error #1009: Cannot access a property or method of a null object reference.

[URL=“http://web.ics.purdue.edu/~mpetkov/3.fla”]