The system does not allow the transfer of an employee that has a different tax code. This is because it is classed as a different place of work and HMRC require you to terminate and then re-employ under the correct tax code.
To check all payrolls listed on the system and their tax reference, follow the steps below:
Go to Settings, usually in Configuration or Admin Menu.
Click on Module Settings then click Payroll Settings.
Click Payroll.