In this case, make sure that you have select the specific business, selecting Options this is going to display the business name, so you can check that you have just 1 name. If you still get a problem, generate a backup data folder and reinstall the program.. To do the backup data folder select Tools /Backup data folder/ generate a folder that would contains all the information of invoices and business.
Then reinstall the program https://www.nchsoftware.com/invoice/eisetup.exe
You can restore later the information selecting Tools/Restore then select the folder previously created. If you still getting problems after this, is better that sumit a request on the technical support page https://www.nch.com.au/support/supportcontact.html?software=ExpressInvoice