Replication Broken After Upgrade From 5.1 => 5.5 (no replies)

Hi,

I've had replication set up between a pair of 5.1 servers for a long time. I just upgraded these servers to 5.5 and now I can't get replication to go again. I tried re-setting the replication user's password, and I even did a complete data reload on the slave. I can connect from the slave to the master using the replicator's credentials without incident. But, when I run "slave start", I get:

mysql> show slave status \G
*************************** 1. row ***************************
Slave_IO_State: Connecting to master
Master_Host: master
Master_User: replicator
Master_Port: 3306
Connect_Retry: 60
Master_Log_File:
Read_Master_Log_Pos: 4
Relay_Log_File: foo-relay-bin.000001
Relay_Log_Pos: 4
Relay_Master_Log_File:
Slave_IO_Running: Connecting
Slave_SQL_Running: Yes
Replicate_Do_DB:
Replicate_Ignore_DB:
Replicate_Do_Table:
Replicate_Ignore_Table:
Replicate_Wild_Do_Table:
Replicate_Wild_Ignore_Table:
Last_Errno: 0
Last_Error:
Skip_Counter: 0
Exec_Master_Log_Pos: 0
Relay_Log_Space: 107
Until_Condition: None
Until_Log_File:
Until_Log_Pos: 0
Master_SSL_Allowed: Yes
Master_SSL_CA_File: /var/db/mysql/ssl.crt
Master_SSL_CA_Path:
Master_SSL_Cert: /var/db/mysql/ssl.crt
Master_SSL_Cipher:
Master_SSL_Key: /var/db/mysql/ssl.key
Seconds_Behind_Master: NULL
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 2005
Last_IO_Error: error connecting to master 'replicator@master:3306' - retry-time: 60 retries: 86400
Last_SQL_Errno: 0
Last_SQL_Error:
Replicate_Ignore_Server_Ids:
Master_Server_Id: 0

Did something break between 5.1 and 5.5? Am I missing something totally obvious here?