cant edit or delete orders - SyntaxError: JSON.parse: unexpe

Hello all,

After much researching all over the web, and obviously in these forums. I have to ask for help as I can’t understand how to solve this problem.
When trying to edit an existing order or manually add an order, I get the following error and can’t go on (SyntaxError: JSON.parse: unexpected end of data at line 1 column 1 of the JSON data OK).
I have tried many solutions available including the following, all to no avail 
- Ensured that maintenance mode is off
- Mod_security is disabled (PHP5.3)
- Created and activated new API User (http://forum.opencart.com/viewtopic.php?f=190&t=135248)
- Changed the user id to match with whats in the database (http://stackoverflow.com/questions/2805 ... 1-column-1)
- Changed the htaccess file (http://forum.opencart.com/viewtopic.php?f=181&t=133490)
I would greatly appreciate all help.

Clean install of Opencart 2.0.1.1
Default Theme
PHP 5.3

Regards