Tested on qa.moodle.org running latest daily Moodle 2.0 PR4 when logged in as a teacher.

Steps to reproduce:

1. Create a new discussion.
2. Attempt to move the discussion.
3. Note that the move button is missing.
4. When the page refreshes, the following error message is displayed:

Could not purge the cached RSS feeds for the source and/or destination forum(s) - check your file permissionsforums

Stack trace:

• line 321 of /lib/setuplib.php: moodle_exception thrown
• line 136 of /mod/forum/discuss.php: call to print_error()

Output buffer: <br /> <b>Warning</b>: opendir(/moodledata/rss/forum) [<a href='function.opendir'>function.opendir</a>]: failed to open dir: No such file or directory in <b>/html/lib/rsslib.php</b> on line <b>84</b><br /> <br /> <b>Warning</b>: readdir(): supplied argument is not a valid Directory resource in <b>/html/lib/rsslib.php</b> on line <b>85</b><br />

A different error is reported by Teresa Gibbison in MDLQA-151.