sql error on install

user warning: Specified key was too long; max key length is 1000 bytes query: subscriptions_install CREATE TABLE subscriptions ( sid int unsigned NOT NULL auto_increment, module varchar(255) default NULL, field varchar(255) default NULL, value varchar(255) default NULL, recipient_uid int NOT NULL, send_interval int default NULL, author_uid int NOT NULL, send_updates tinyint NOT NULL default 0, send_comments tinyint NOT NULL default 0, PRIMARY KEY (sid), KEY (module, field, value), KEY (recipient_uid) ) /*!40100 DEFAULT CHARACTER SET utf8 */ in /Users/mw/htd/dr5/includes/database.mysqli.inc on line 151.