At first, check that the national minimum wage values have been entered by following the steps below:
Go to Setup and click Settings.
Click Module Settings, then Payroll Settings.
Click National Minimum Wage.
Make sure that there are values saved with an effective date equal or previous to the effective date of the employee's salary which you were trying to add. If there aren't any, click Add New Year Without Age Bands to enter them.
Click Save and create employee payment changes.
You should also check the employee's age and make sure there are values entered for that age range.
Once the above has been completed, run a batch update and try again.