You are seeing the below error message on your Desktop Sync App.
Unable to cast COM object of type 'SageDataObjects SDOEngineClass' to interface type 'SageDataObjects.ISDOEngine'. This operation failed because the QueryInterface call on the COM component for the interface with IID failed due to the following error: No such interface supported (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)).
Sage 50 users
This error is related to an issue with your Sage Accounts Data Service.
To resolve this, you will need to contact Sage to check whether your Data Service needs to be uninstalled and reinstalled.
More information on doing this can be found here.