There is an error when I validate the XML file for Appendix 8A. What do I do?

Under File Generation -> Appendix 8A

For each affected employee, click the book icon, and click "Submit and Next" on every page, regardless of whether you edited the page or not.  Then, click the ‘submit’ button. You should be able to see ‘Save Successfully’ above the button when you have done that.

After that, regenerate the file.