Resolving issue with mysql.proc after upgrading MySQL from 5.0.* to 5.1.*
I was having this issue, and thought I'd mention that running "mysql_upgrade --force" fixed it for me.

I upgraded from 5.0 to 5.1 to 5.5.  The interesting this is that I had already run mysql_upgrade which is why I needed to add the --force option.  Hope this helps someone.