The saved file in the MotionBuilder larger than 2GB will not be open in the future. The way out – to save the file, not including the content in it (embedded data).
This plugin is designed to show the notification in the case if you saved the file exceeds 2GB in size.
Download – File Size Checker Installation Package
Supported Autodesk MotionBuilder 2013 (64bits), 2014 (64bits)