Migration from 5.1 to 5.6, get an error replicating a password

[Steve Guntly]

I am looking at upgrading a couple of our older MySQL servers (mysql Ver 14.14 Distrib 5.1.69, for sun-solaris2.10 (sparc) using readline 5.1) to 5.6 (mysql Ver 14.14 Distrib 5.6.13, for solaris11 (sparc) using EditLine wrapper).

I first created a dump of all our databases on the 5.1 server. I then imported the dump and ran mysql_upgrade on the new 5.6 server. I then set up slaving with the 5.1 server as the master (using the correct bin-log and location).

The replication started out fine, but then stopped with this error:

Last_Error: Error 'Password hash should be a 41-digit hexadecimal number' on query. Default database: 'mysql'. Query: 'SET PASSWORD FOR 'webdbadmin'@'%'='(16 digit hex number removed for security purposes)''

When I check this user on the master server, it does have a 16 digit hash. On both the master (5.1) server and the slave (5.6), I have old-passwords = 1 set. I also checked the running variables:

Variable_name: old_passwords
Value: 1

Is there any other settings I need to set on the new 5.6 server so that it'll accept this from the master?

Thanks