Can't Modify customer orders after upgrade to 2.0.x

I went through the whole upgrade process from Opencart 1.4.x to 1.5.x to 2.0.1 and after following all the instructions in the upgrade documentation, everything seems to be ok except for the fact that I can't modify order statuses or change customer orders in any way shape or form. when i go to edit an order, all of the modules are grayed out, and no matter what i click i get an error message saying

SyntaxError: JSON Parse error: Unrecognized token '<'
OK
<b>Notice</b>: Use of undefined constant HTTPS_CATALOG - assumed 'HTTPS_CATALOG' in <b>/home/content/96/7448396/html/admin/controller/sale/order.php</b> on line <b>2441</b>

Make sure that the /admin/config.php file has the following line

the https was missing in the admin config, however that doesn't solve the problem.... I still get

SyntaxError: JSON Parse error: Unrecognized token '<'
OK
<b>Notice</b>: Undefined variable: json in <b>/home/content/96/7448396/html/admin/controller/sale/order.php</b> on line <b>2221</b>

I don't think it has been upgraded properly.

Make sure there is an API user here And it is also selected here:

KineticConsulting wrote:the https was missing in the admin config, however that doesn't solve the problem.... I still get

SyntaxError: JSON Parse error: Unrecognized token '<'
OK
<b>Notice</b>: Undefined variable: json in <b>/home/content/96/7448396/html/admin/controller/sale/order.php</b> on line <b>2221</b>

There are 2 reasons this happens...
1. If you didn't add an API user like deepvision mentioned.
2. Your host disabled HTTP Loopback on your site and you need to use this work around:
http://forum.opencart.com/viewtopic.php?f=2&t=146714

ok i have verified there is an api user added and selected for my store, and also uploaded vqmod, and the loopback script, and I am still having the same problem. any further suggestions?

A lot of things might have gone wrong during upgrade.
No more errors in the error log? Especially right before the one you posted.

@deepvision

When I go to system>users>api
I dont see any users


ERROR LOG

2015-07-24 2:35:17 - PHP Notice: Undefined variable: json in /home/public_html/admin/controller/sale/order.php on line 2490
2015-07-24 2:35:29 - PHP Notice: Undefined variable: json in /home/public_html/admin/controller/sale/order.php on line 2490

@kevtheirish:

You should add an API user and choose it here: System -> Settings -> Your store -> Option -> API user