This sync error appears when the invoice that was exported has been coded to an account that does not exist in your Sage 50 US. Likely, the account was deleted.

Check in your Sage 50 US to see if you can locate that account in your ERP. 

If the account is not there, please reset the invoice and update the account to one that is available in Sage 50 US. Since Beanworks can only pick up with accounts are deactivated (not deleted), please contact Support to deactivate the deleted account. 

If the account is in your Sage 50 US, please contact Support.