Cannot change X-Frame-Options

#1

I want to allow my website to be iframed by other websites so I try to set the X-Frame-Option to ALLOWALL
I did it by editing the .htaccess file and also the web.config file
.htaccess
Header always append X-Frame-Options ALLOWALL
web.config

<httpProtocol>
    <customHeaders>
      <add name="X-Frame-Options" value="ALLOWALL" />
    </customHeaders>
  </httpProtocol>

Still, i get this error…

Multiple ‘X-Frame-Options’ headers with conflicting values (‘ALLOWALL, SAMEORIGIN’) encountered when loading "…’. Falling back to ‘DENY’.

It seems that something sets this X-Frame-Option to be SAMEORIGIN.
How can I override it?
Thanks in advanced guy!

#2

What is your website?

#3

Removed X-Frame-Options ALLOWALL from server headers

#4