I can't install any new plugins or themes on a clean install of WordPress 2.9.2 on Mac OS X 10.6.2. When I do, I get the following message:
Warning: array_keys() expects parameter 1 to be array, boolean given in /Users/cvhyphus/Sites/yessounds/yessounds.org/trunk/public_html/wordpress/wp-admin/includes/class-wp-upgrader.php on line 188
Plugin Install Failed.
I've tried using a completely clean install from a freshly-downloaded copy of WordPress 2.9.2. I tried installing renamed copies of Akismet and of the default theme, as well as trying to install the themes and plugins I actually want to install. I looked through similar posts here, but hadn't found any with this particular issue.
The wp-content subdirectory has _www as a group owner, and this directory and everything inside of it is writable by both the user and this group (i.e. chmod -R 775 wp-contents), which fixed complaints that the contents of this directory were not writable). The attempted installs from the admin panels is using ftp to localhost, which is set up and working perfectly.
Manually unzipping these themes and plugins and themes and placing them in the plugins or themes directories as appropriate successfully installs them. An attempt to automatically upgrade the "Contact Form 7" plugin "automatically" failed in the same way. Manually installing it worked fine.
As eventually I'm going to have this all hosted on a remote server after I finish developing a custom theme and a couple of plugins, I would like to be able to use this functionality. I've only seen this problem on my local Mac OS X; I have not had any problems with my existing WP 2.9.2 installations hosted on CentOS 5.