This error comes when you are trying to connect Unify Enterprise to your QuickBooks company file and a window / prompt / dialog box / screen open in QuickBooks. That prevents Unify Enterprise from connecting to QuickBooks.
How to fix:
1) Go to QuickBooks,
2) Close the window/ prompt /dialog box
3) Make sure you can view the QuickBooks home screen and
4) Attempt to connect Unify Enterprise again