Problems submitting payroll info to HMRC

I've just processed a payslip for this month, but it won't submit it to HMRC. Any ideas?

See error message:

There were one or more validation issues that need to be addressed before this FPS can be submitted to HMRC

Element '{http://www.govtalk.gov.uk/taxation/PAYE/RTI/Full Payment Submission/17-18/1}Pmt Date': [facet 'min Inclusive'] The value '0017-05-16' is less than the minimum value allowed ('2017-04-06'). Element '{http://www.govtalk.gov.uk/taxation/PAYE/RTI/Full Payment Submission/17-18/1}Pmt Date': '0017-05-16' is not a valid value of the local atomic type.