Sage 50 and Shipgear connection error

SOLVED

My client is running the latest Sage 50 US 2021 and Shipgear 10 (also latest version). We are unable to connect Shipgear to our main company file. Connects fine to other company files, just not this one. Sage support has not been able to help us, nor has Shipgear. 

The problem has been ongoing. We were running Sage 2017 on a Windows Server 2008 and have recently moved our Sage installation to a dedicated Win 10 Pro workstation. The problem predates the migration. The method we used to migrate was to back up our company file on the old server, then restore to the new Sage host. Everything else works in the new Sage.

Thanks for any help you can provide!