37

I fixed this by going through PHPMyAdmin to the table “Options” and then the row active_plugins.

I had the following stored there (formatted for readability):

a:10:{
    i:0;s:49:"1and1-wordpress-wizard/1and1-wordpress-wizard.php";
    i:1;s:29:"acf-repeater/acf-repeater.php";
    i:2;s:30:"advanced-custom-fields/acf.php";
    i:3;s:45:"limit-login-attempts/limit-login-attempts.php";
    i:4;s:27:"redirection/redirection.php";
    i:6;s:33:"w3-total-cache/w3-total-cache.php";
    i:7;s:41:"wordpress-importer/wordpress-importer.php";
    i:8;s:24:"wordpress-seo/wp-seo.php";
    i:9;s:34:"wpml-string-translation/plugin.php";
    i:10;s:38:"wpml-translation-management/plugin.php";
}

I added a new line (for the missing plugin) and incremented the a:10 to a:11 to indicate that there are now 11 items in the array:

a:11:{
    i:0;s:49:"1and1-wordpress-wizard/1and1-wordpress-wizard.php";
    i:1;s:29:"acf-repeater/acf-repeater.php";
    i:2;s:30:"advanced-custom-fields/acf.php";
    i:3;s:45:"limit-login-attempts/limit-login-attempts.php";
    i:4;s:27:"redirection/redirection.php";
    i:5;s:40:"sitepress-multilingual-cms/sitepress.php";
    i:6;s:33:"w3-total-cache/w3-total-cache.php";
    i:7;s:41:"wordpress-importer/wordpress-importer.php";
    i:8;s:24:"wordpress-seo/wp-seo.php";
    i:9;s:34:"wpml-string-translation/plugin.php";
    i:10;s:38:"wpml-translation-management/plugin.php";
}

i: appears to be item number, and thanks to JHoffmann’s comment, it appears s: is the length of the string that follows.

The site now works as before!