Hi robcraw,
Thank you for your post and sorry to hear you're running into this issue.
Generally speaking, this error occurs if you attempt to resume a previously 'saved' pay run - but changes have been made after the pay run was created and saved. To get past this error you will need to discard the saved pay run and create a new one.
However, if this is not a saved pay run and you're still experiencing this error, could you please locate your Diagnostic log and attach it in your reply?
If my response has answered your enquiry please click "Accept as Solution" to assist other users find this information.