Attempting to update Shopp through the WordPress Dashboard Updates area will result in an error. Update your Shopp software through WordPress Plugins.
An error occurred while updating Shopp: The package could not be installed. PCLZIP_ERR_BAD_FORMAT (-10) : Unable to find End of Central Dir Record signature.
This will occur if you try to update Shopp through WP-admin → Dashboard → Updates.
Shopp is not hosted in the WordPress plugins directory.
To correct this issue, go to WordPress Admin → Plugins. Then locate Shopp in your list of plugins and click Update.