Cant install Ajax registration

I get this error:



        JInstaller: :Install: Error SQL DB function failed with error number 1005
        Can't create table '48_hopsms.o38y2_ajaxregister_field_values' (errno: 121) SQL=CREATE TABLE o38y2_ajaxregister_field_values ( `user_id` int(11) NOT NULL, `field_id` int(11) NOT NULL, `value` varchar(255) NOT NULL, KEY `idx_user_id` (`user_id`), CONSTRAINT `values_ibfk_1` FOREIGN KEY (`field_id`) REFERENCES `o38y2_ajaxregister_fields` (`id`) ON DELETE CASCADE ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='AJAX Register fields value storage table';
        SQL =

        CREATE TABLE #__ajaxregister_field_values (
          `user_id` int(11) NOT NULL,
          `field_id` int(11) NOT NULL,
          `value` varchar(255) NOT NULL,
          KEY `idx_user_id` (`user_id`),
          CONSTRAINT `values_ibfk_1` FOREIGN KEY (`field_id`) REFERENCES `#__ajaxregister_fields` (`id`) ON DELETE CASCADE
        ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='AJAX Register fields value storage table';

        Component Install: SQL error file DB function failed with error number 1005
        Can't create table '48_hopsms.o38y2_ajaxregister_field_values' (errno: 121) SQL=CREATE TABLE o38y2_ajaxregister_field_values ( `user_id` int(11) NOT NULL, `field_id` int(11) NOT NULL, `value` varchar(255) NOT NULL, KEY `idx_user_id` (`user_id`), CONSTRAINT `values_ibfk_1` FOREIGN KEY (`field_id`) REFERENCES `o38y2_ajaxregister_fields` (`id`) ON DELETE CASCADE ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='AJAX Register fields value storage table';
        SQL =

        CREATE TABLE #__ajaxregister_field_values (
          `user_id` int(11) NOT NULL,
          `field_id` int(11) NOT NULL,
          `value` varchar(255) NOT NULL,
          KEY `idx_user_id` (`user_id`),
          CONSTRAINT `values_ibfk_1` FOREIGN KEY (`field_id`) REFERENCES `#__ajaxregister_fields` (`id`) ON DELETE CASCADE
        ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='AJAX Register fields value storage table';

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What can be wrong ?

What's your mySQL version?