Mahmoud explains a Document Attachment Error with GP 2015 R2 Resolved with July Hotfix Round 2
Dynamics GP Essentials: Document Attachment Error with GP 2015 R2 – Resolved with July Hotfix Round 2
Install, Upgrade & AdminGP 2015
Archived post from 2015. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.