Multi-DB and WP plugins that can't find/make their tables

I'm setting up a site with Multi-DB. Most of it has gone smoothly, but there are some (Wordpress, not Wordpress MU) plugins that can't seem to find/make the tables they require.

The plugins are NextGEN Gallery and Event Calendar.

For NextGEN, a look at the database shows that the tables have been created. However, it keeps saying that the tables could not be created. The code that outputs the error is in the function nggallery_install() in ngginstall.php:
if($wpdb->get_var("show tables like '$nggpictures'")!= $nggpictures) {
update_option( "ngg_init_check", __('NextGEN Gallery : Tables could not created, please check your database settings',"nggallery") );

For Event Calendar, it says there was an error creating the tables. The tables don't appear in the database. The code that produces the error is in function upgrade_database() in file admin.php:
$tables=$wpdb->get_results('SHOW TABLES',ARRAY_N);
die(sprintf(__('Error upgrading database for %s plugin.','ec3'),