David Musgrave has a Quick Tip: VBA ADO Connection Run-time error ‘3709’
Quick Tip: VBA ADO Connection Run-time error ‘3709’ – Developing for Dynamics GP – Site Home – MSDN Blogs
Tips & Hidden FeaturesInstall, Upgrade & AdminDevelopment & Integration
Archived post from 2013. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.