This is an issue with updated DLLs in Office 2016 conflicting with third-party software applications, including AbacusLaw by CARET. The solution is to delete the Abacus Outlook add-in DLLs, and update AbacusLaw by CARET.
Delete the Outlook add-in DLLs, located in SysWOW64:
- Change to Install mode and run the AbacusLaw by CARET update as admin.
- Once done and back in Execute mode, test by opening and closing both Outlook and AbacusLaw by CARET as the user at least three times.