Troubleshooting: Can't install plugins
Sometimes problems can occur with the installation because of permissions, depending on your server configuration. To solve the problem you may temporary set the permissions recursively on your /wp-content and sub-folders to 777. But this is not safe, so do not forget to back permissions to 755. For more information please visit the codex.
If changing permissions did not help and you still have issues with automatic plugin installation try to install them manually. You can find bundled plugins in theme's /plugins sub-directory. You should extract plugins from the archives and upload them, e.g. through FTP to /wp-content/plugins/ directory.