Over at Developing for Dynamics GP David Musgrave shows How to display more than 80 characters of an Extender Long String field in reports using the Support Debugging Tool.
How to display more than 80 characters of an Extender Long String field in reports using the Support Debugging Tool – Developing for Dynamics GP
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Archived post from 2011. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.