I am getting the next error after i give a new category or tag on my small publish_type:

Uncaught TypeError: Cannot read property 'supplemental' of undefined - load-scripts.php:5

I can not see anything in /wp-admin/load-scripts.php that will cause that error (fresh install of recent WordPress 3.2.1 here). Maybe someone or something like that has modified the script which is not suggested, or you are running an outdated version of WordPress, or both.

As it is a core file I'd recommend re-installing WordPress, or at best improving it. Which will overwrite your overall load-scripts.php having a working copy.

I have just had exactly the same problem, and irritatingly enough it had been a whitespace character prior to the opening PHP tag inside a file I incorporated in functions.php. It appears to become invalidating the ajax / json response.

I recommend searching at any stray whitespaces pre and post the tags.

Advisable would be to your investment closing ?> tag on functions.php and then any incorporated files this removes the risk of a personality getting into.

Hope this can help...