Trackbacks are often abused by SpamBots and may cause various problems. That's why you are advised to disable trackbacks until you are certain you can deal with all complications which may follow.
In order to disable trackbacks in WordPress, go to your Admin panel, Options, Discussion tab. There uncheck "Allow link notifications from other blogs (pingbacks and trackbacks.)"
You can also disable this feature by this SQL query:
UPDATE wp_options SET option_value = 'closed' WHERE wp_options.option_id =20 AND wp_options.blog_id =0;