I have found about about an error that happens with the default install for 0.9.6. But it took me ages to find out about. So I am listing it here, sorry if this is not helpful.
When you have the template switcher plug-in installed. Read more about it below: (Content from
http://modxcms.com/forums/index.php/topic,14661.0/wap2.html)
Caspian: I’m new to MODx... so please be understanding if this is a dumb question

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I’ve marked my documents as cacheable, but they all say "This document has not (yet) been cached." Is there something I need to do in order to cache documents?
Thanks.
Mark:It takes one page load for the document to cache. Once the page has been requested, MODx will cache the page so long as assets/cache is writeable.
Caspian: Ok, I’ve found a solution to my problem, although it’s a hack. If I edit siteCache.idx.php and delete the content (except for the first 100 lines or so, which are page definitions), pages become cached (I can see files being added to assets/cache). However, once I clear the cache through the MODx admin panel, all the content comes back into siteCache.idx.php. (The content appears to be stuff for snippets that I don’t use anyways) but once this happens, none of my pages are cached anymore.
Is the "siteCache" file somehow keeping my pages from being cached? Is this a bug, or am I supposed to do something else to enable caching?
I’m using MODx 0.9.5, PHP 5, and MySQL 14.12.
rthrash: Do not edit the siteCache or .idx files or you’re asking for problems most likely. I suspect you have the template switcher plugin installed. Delete it.
Caspian:Thanks... that did the trick! I restored my siteCache file from a backup and deleted the template switcher plugin. Pages are being cached now. Thanks!
redman: good info, thanks.
sirlancelot: siteCache.idx.php is recreated every time cache is cleared, but editing it is a big no-no