Mariano latest post looks at Unhandled script exception: Illegal address for field ‘[Not Found]’ in script ‘Unregister_Triggers’
The Dynamics GP Blogster: Unhandled script exception: Illegal address for field ‘[Not Found]’ in script ‘Unregister_Triggers’
Archived post from 2011. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.