Every time I attempt to upgrade a plugin, no matter if it's activated or not, I get the following message:
Example plugin, Wordpress Popular Posts (this happens with every plugin ever since the 2.8.1 upgrade from 2.8):
Downloading update from http://downloads.wordpress.org/plugin/wordpress-popular-posts.1.5.1.zip.
Unpacking the update.
Incompatible archive PCLZIP_ERR_BAD_FORMAT (-10) : Invalid archive structure