But theres some problem

When i try t oadd my site to google sitemaps and verify it by clicking the verify button it says this

We've detected that your 404 (file not found) error page returns a status of 200 (OK) in the header.
:
This configuration presents a security risk for site verification and therefore, we can't verify your site. If your web server is configured to return a status of 200 in the header of 404 pages, and we enabled you to verify your site with this configuration, others would be able to take advantage of this and verify your site as well. This would allow others to see your site statistics. To ensure that no one can take advantage of this configuration to view statistics to sites they don't own, we only verify sites that return a status of 404 in the header of 404 pages.


What may be the problem ?