[wp-hackers] Throwing An Error And Not Saving When Metabox Input Is Wrong

[Ken (WraithKenny)]

there are a couple of viable answers here
http://wordpress.stackexchange.com/questions/15354/passing-error-warning-messages-from-a-meta-box-to-admin-notices

A third option is to append a new message variable to the url (say
"&metabox_message=3"), then on the admin_notices hook, use a lookup
like wp does (its an array of messages on the "3" would be the index)
or however you like.