Hello!
It's me, again.
This error message I've got after I've tried to deactivate WordPress OpenID Plugin
WordPress database error: [Specified key was too long. Max key length is 500]
CREATE TABLE wp_openid_associations ( server_url varchar(255) CHARACTER SET latin1, handle varchar(255) CHARACTER SET latin1, secret blob, issued int(11), lifetime int(11), assoc_type varchar(64), PRIMARY KEY (server_url(255),handle) )
WordPress database error: [Duplicate key name 'server_url']
ALTER TABLE wp_openid_nonces ADD UNIQUE KEY server_url (server_url(255),timestamp,salt)
WordPress database error: [Unknown table 'wp_openid_associations']
drop table wp_openid_associations
WordPress database error: [Unknown table 'wp_openid_settings']
drop table wp_openid_settings
Warning: Cannot modify header information - headers already sent by (output started at /mywebsite_path/wp-includes/wp-db.php:133) in /mywebsite_path/wp-includes/pluggable.php on line 329
It was deactivated anyway.