Can’t save plugin filter

You can run this statement on your database to create the table. Replace -DB_PREFIX- with your wordpress table prefix.

CREATE TABLE -DB_PREFIX-po_plugins (
			pl_id bigint(20) unsigned NOT NULL AUTO_INCREMENT,
			post_id bigint(20) unsigned NOT NULL,
			permalink longtext NOT NULL,
			permalink_hash varchar(32) NOT NULL default '',
			permalink_hash_args varchar(32) NOT NULL default '',
			post_type varchar(255) NOT NULL default '',
			status varchar(20) NOT NULL default 'publish',
			secure int(1) NOT NULL default 0,
			children int(1) NOT NULL default 0,
			pt_override int(1) NOT NULL default 0,
			disabled_plugins longtext NOT NULL,
			enabled_plugins longtext NOT NULL,
			disabled_mobile_plugins longtext NOT NULL,
			enabled_mobile_plugins longtext NOT NULL,
			disabled_groups longtext NOT NULL,
			enabled_groups longtext NOT NULL,
			disabled_mobile_groups longtext NOT NULL,
			enabled_mobile_groups longtext NOT NULL,
			post_priority int(3) NOT NULL default 0,
			dir_count int(3) NOT NULL default 0,
			user_role varchar(255) NOT NULL default '_',
			PRIMARY KEY (pl_id),
			KEY PO_post_id (post_id),
			KEY PO_permalink_idx (permalink_hash,status,secure,post_type,user_role),
			KEY PO_permalink_args_idx (permalink_hash_args,status,secure,post_type,user_role),
			KEY PO_page_lists (post_id,post_type,user_role)
		);

The biggest key I see is 566 bytes.

You can also change your collation to something like utf8_general.