There is a good summary of how to debug "Access Denied" problems at http://dev.mysql.com/doc/refman/5.0/en/access-denied.html. It's a bit long, so you may want to start with careful attention to the item about a third down the page, which talks about how permissions with a "%" wildcards for host can supercede an explicit entry for "localhost". The way this works is counter-intuitive at first, and it is an easy mistake to make.

I appologize in advance to anyone bothered by my answering this off topic question here. I just suspected there are other people like me who are doing primarily Perl, and doing only as much MySQL as they need to. For us, finding the answer to a simple problem with the MySQL documentation can be a little like trying to get a sip of water from a fire hose.