After much troubleshooting, the problem seems to come from 64-bit Office installations conflicting with Acrosoft's 32-Bit MAPI interface.
We have recently solved the issue of MAPI errors coming up for Acro Docs/WM users when attempting to send a file via email from within Acrosoft products.
How to Uninstall 64-Bit Office/Reinstall 32-Bit Office on Windows 10 (Acro/Hyland Mail/MAPI issue)