I had to do some changes because of the TimThumb vulnerability, and I think it started after that.
The Theme Editor links to a blank cached version of my index. This is the URL I see at the top:
http://mysite.com/wp-admin/theme-editor.php?file=%2Fthemes%2Fjellybeantheme%2Fcache%2Findex.php&theme=My+Site&dir=theme
If I remove the "%2Fcache" parameter from the URL it takes me to the correct index.php
Anyone have any help?