In troubleshooting I have made the following observations:
I am able to edit and delete existing webparts on the page. Only "add a webpart" is broken.
My collegues at work have no issues with adding webparts.
I am able to add webparts in the dev environment so the problem is only in production.
I get the same issue using Chrome, Firefox, and IE8.
I tried clearning my cache and deleting all my temp files but the issue is still there.
Does anyone have any ideas on what could be causing this and how I can fix it?