WordPress Page Update - 403 Forbidden

Dear all,
I am facing a problem after the installation of a new WordPress site.  I can update the "Post" by creating new / updating.

Forbidden
You don't have permission to access /wp-admin/post.php on this server.

Unfortunately, I can't do anything on top of pages.  Currently, I have disabled nearly all plugins but only the classic editor.

I have used the "Fix Permission" function in the CWP and checked the folders / files as 755 for the wp-admin and php files within it as 644.  Could anyone suggest any clues?

Thanks.
Regards,
AbsoluteMusik

is modsecurity enabled?

I had the same issue for /wp-admin/nav-menus.php when trying to create a new menu.

I disabled mod security for that particular domain in my CWP and it was working after that. (But i don't know whether its safe to leave it like that)

It worked for me as well...so is there another solution I have used the fix permission many times and did not do anything for my case. Thank you very much.

IF you want to do this properly then check the mod_sec log just after the the problem arises. It will show the rule ID.
Remove that particular rule from the account's mod_sec settings - there's even a GUI in admin to help you do so.
You might want to exclude it globally and CWP provides a few by default, so you even get to see the syntax.
Couldn't get much easier, if you care to look/try.

when I check IP address, in the case my own IP-

I get the message:

Ip not found in /usr/local/apache/domlogs/misanthropicradio.com.error.


Thank you very much

..
Ip not found in /usr/local/apache/domlogs/misanthropicradio.com.error.
..

No-one mentioned Apache dom logs. 
It's a mod security issue.

.. there's even a GUI in admin to help you ..

When I faced some of these same type issues, I found there was an endless supply of rule IDs to fix in modsec. I saw a note somewhere that switching to Comodo WAF in modsec would solve that issue and indeed it did.