What I think is that the database you are trying to dump contains procedures/methods that were defined by a user while logged in as root@'foobar'.
Now the solution is that you have to replace the definer's for that procedures/methods
then you can generate the dump without the error.
you can do this like ..
UPDATE `mysql`.`proc` p SET definer = 'root@localhost' WHERE definer='root@foobar'
Be careful, because this will change all the definers for all databases.
UPDATE on 9th Feb 2012
As I saw the link given by @gbn which is an answer given by @Rolando that can also be the Case. Please visit the link
EDIT by @RolandoMySQLDBA 2011-12-16 11:20 EDT
While risky, this answer is good. Just to clarify: You can specify the database in your query like this:
UPDATE `mysql`.`proc` p SET definer = 'root@localhost' WHERE definer='root@foobar' AND db='whateverdbyouwant';