Forbidden to update wp-admin/post.php

I just wonder if anyone has the same problem. Previously when the domain is not yet purchased, I’m using the server ip address to access the website. The website is using wordpress 3.5.

When i have brought the domain, I have downloaded the whole database and replaced all the absolute path to the server ip to domain name. I did not have any problem with previous wordpress version (3.0 and 3.4) using the same replacing method. The website is loading fine and able to add in new post and page. But when it comes to upload a new photo and save/update the post/page, it show Forbidden error Forbidden You don’t have permission to access wp-admin/post.php on this server.
I have tested. If the img source have absolute path eg. http://www.domainname.com/wp-content/uploads/2013/02/imagename.jpg, and i clicked Save/Update the post, it will show this error. But if i removed the domain name eg. /wp-content/uploads/2013/02/imagename.jpg, I have no problem save/update the post.

I don’t have any idea what cause the problem. I have add in the .htaccess as what highlighted in some other forum. But that did not solve the problem.

Then some people suggest might be the theme or plugins that cause the problem.

So i uploaded the whole website with the same theme and plugins to a subfolder. Created a new database and imported the tables from the previous database and updated the all the absolute path records to the path of the subfolder. Then i tried to upload and image and save. No problem at all! Same thing if i update the post with other images. The
images source is full absolute path eg. http://www.domainname.com/wp-content/uploads/2013/02/imagename.jpg

Does anyone have any idea how to solve this problem?

I’m using wordpress 3.5.1 with Responsive Theme version: 1.8.9.3 (from ThemeID) calling the child theme Responsive Child Theme version 1.0.0