That's very strange, because I use all of those plugins on my personal site, and Code Snippets is working fine. I'm not using those themes, though. If it's no imposition, would you be able to post the source code of the page in between the
<div class="wrap" opening and closing tags (or the whole page source) either on GitHub or Pastebin or similar? It would make debugging this issue a whole lot easier.
Errors like this usually occur when two different versions of CodeMirror (which powers the textarea) are loaded on the same page. This wasn't an issue when Code Snippets used CodeMirror 2 (which is used by many old plugins that use CodeMirror), but version 1.6 and up use CodeMirror 3.