Custom jQuery $.post 403

Hey,

So to keep this simple – I have created a bit of jquery code, and some custom fields on the posts page to dynamically load in my form elements.

So when I load up the form, I want it to create a category based on the input I put in, without leaving the posts page.

Eveytime I click my submit button, it starts up the jquery easily enough, but when it gets to the $.post part it spits back a 403 forbidden.

When I update the permissions from 755 to 777 to test I get server 500 errors.

The steps I have tried are thus –
Building the code into the functions file to load my specific javascript.
Deleted, and emptied out my htaccess file.
Turned on wp_config
Disabled plugins

I am at a stand still, I don’t know what could be causing this. Any help would be greatly appreciated.