This worked for me :
This can occur when you’re running W3 Total Cache and you’ve ticked the setting to hide the sitemap from normal visitors. What W3TC does is cache the error which normal visitors get, if they want to view the video XML sitemap. This error is then also served to googlebot, because the logic to show the sitemap to googlebot won’t execute. The best way to fix this is to create an extra user agent group.
You can create this user agent group by going to the W3TC’s settings. Under Performance and then User Agent Groups there’s a button “Create a group”. Click this button and call your group “Google” or “Googlebot” and then in the user agents field you just enter “googlebot”. This will force W3 Total Cache to make a separate cache for Googlebot user-agents. Another option is to prevent W3TC from caching video-sitemap.xml entirely, but since that’s slower, we actually prefer the user-agent group.
