If you receive an error email telling you that Commusoft was unable to send data across to Sage because this username is already in use, it is because Sage was open at the time of the import.
Please close Sage to allow Commusoft to send data.
Essentially, when Commusoft sends data to Sage, it logs in with your username. If this username is logged in elsewhere, Commusoft cannot connect.
Closing Sage will allow Commusoft to connect and send your data