How to fix "409 conflict" after validating?

EDITED TO UPDATE: PAGE VALIDATES NOW (NO IDEA WHY) BUT WOULD STILL LIKE TO KNOW WHAT THE “409 CONFLICT” MEANS.
All pages on my website validate just fine except one. I get this message from W3C Validation Service: “Sorry! This document cannot be checked!” and states “409 conflict.” But there’s nothing to tell me how to fix it so it will check and validate. Help on this riddle will be appreciated! Thank you.

Usually when you encounter a bug, term, or phrase you don’t know, a web search can lead you in the right direction:

In the future, if you have issues on specific pages, links to them (and the challenges they are based on) are helpful, as is quoting specific code that you believe is relevant.

Thank you. I did do a web search for it and found it not-helpful. There was no indication as to which code is relevant. I was hoping someone had experience with it to tell me what it might mean. Somehow or other it resolved itself. (I like duckduckgo. Never tried it before!)