Why did you receive the error?
This error occurs because your RosterElf Payroll Cycle is set to weekly but your Xero account's Payroll Cycle is set to fortnightly. A warning message as per below will indicate this is the issue.
How do you fix this issue?
You will need to log into your Xero account and review all the employee files under the "Employment" tab to ensure they have a "Payroll Cycle" set to weekly as per your RosterElf settings. Alternatively, if you need to have a Fortnightly payroll cycle, you will need to update your RosterElf account to fortnightly which you can read about how to do HERE.