This question already has an answer here:
I just want to save my preferred domain as
www.example.com in Webmaster Tools but it simply shows the following error message:
Part of the process of setting a preferred domain is to verify that you own
http://example.com/. Please verify
I can't save the setting, any idea why this is happening?
Note: I already verified the www version, I have no idea to verify the no-www version.