If you’ve ever seen this error when trying to install a plugin in your WordPress Admin Panel, you have probably considered going on a murderous rampage:

“The plugin does not have a valid header.”

This error is probably due to your list of Plugins being cached in whatever WP Object Cache your blog / site is using. None of the sites you will find when searching Google will tell you this. They will tell you that you have an invalid Plugin Header. You might. But probably, your list of files is cached.

There are 2 problems here:

1) The list of plugins ( $cache_plugins ) is not pluggable

2) the generic error for all missing plugins is “The plugin does not have a valid header”

function validate_plugin($plugin) {
    if ( validate_file($plugin) )
        return new WP_Error('plugin_invalid',
            __('Invalid plugin path.'));
    if ( ! file_exists(WP_PLUGIN_DIR . '/' . $plugin) )
        return new WP_Error('plugin_not_found',
            __('Plugin file does not exist.'));

   $installed_plugins = get_plugins();
   if ( ! isset($installed_plugins[$plugin]) )
       return new WP_Error('no_plugin_header', 
           __('The plugin does not have a valid header.'));
   return 0;
}

TO FIX THIS GARBAGE = in /wp-admin/includes/plugin.php at line 219-ish, comment out the lines below then visit your Plugins list:

// if ( ! $cache_plugins = wp_cache_get('plugins', 'plugins') )
$cache_plugins = array();

// if ( isset($cache_plugins[ $plugin_folder ]) )
// return $cache_plugins[ $plugin_folder ];

When you’re done and everything works, un-comment those lines. If this didn’t fix the problem, then yes, you probably fucked up when creating the Plugin header comment.