This is normally because of the code placed Google, Yahoo or Bing Verification. They should not contain any HTML coding when placed in your admin panel. Only the code itself.
To remove this, go to Settings > Store Settings > SEO Settings. In the relevant verification field, remove all HTML codes:
(This is an example code)
<meta name="msvalidate.01" content="B551F5796A9EU6EDE8DBA001FB790462" />
But leave only B851F5796A9EU6EDE8DBA101FB790462
So it should be written as: .... Verification Code: B851F5796A9EU6EDE8DBA101FB790462
Once done, click "Save Changes"
