This means that the current version of Sage that your company file is associated with does not match the version of the Accounting Connector.
Step 1 to check have you upgraded the Accounting Connector, should have a pop up when opening it on your desktop to click yes to upgrade.
Step 2 to check do you have the newest version of Sage.
Step 3 to check has your company file been opened in the new version of Sage.