Kelly Youells covers some issues with the Collections Management Upgrade to Microsoft Dynamics GP 2013 Version 12.00.1343
Collections Management Upgrade to Microsoft Dynamics GP 2013 Version 12.00.1343 – Dynamics GP Support and Services Blog – Microsoft Dynamics GP – Microsoft Dynamics Community
Microsoft & the GP EcosystemPayables & ReceivablesInstall, Upgrade & AdminGP 2013
Archived post from 2013. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.