Sorry this is WP 2.7. If I log out and log back in after a bad plugin install, the issue gets worse and I get more errors that are similar. It is as if the plugin install tries something that doesn’t finish, and the application can’t function until it is taken care of.
If I uninstall the plugin so that I can finally get to the site, and then go to the Plugin Page in Administration, it gives an error saying the newly installed plugin cannot be found, and it is not listed in my list of plugins.
At this point I can install the plugin MANUALLY and it seems to work.