This error is usually caused by an issue with the file named - 'AccessAccounts.AccessOfficeIntegration.SharedSettings.xml'
This is located in the Appdata folder, and is best fixed by allowing AOI to regenerate the file.
To do this, please follow these steps:
Open a new File Explorer window.
Delete the navigation path from the Address bar at the top.
In the Address bar enter '%appdata%'. Press Enter.
The file path to the ‘Roaming’ folder appears.
Open the AccessAccountingLtd folder.
Open the AccessOfficeIntegration folder.
Open the folder corresponding to the AOI version being used currently.
Delete the file AccessAccounts.AccessOfficeIntegration.SharedSettings.xml
Open AOI Administrator, this will remake the previously deleted file and AOI will now be working correctly.
Note : Any Office products that were previously ticked on the Options page will need to be re-ticked.