The mysql_upgrade program tries to realign the mysql.user table with latest grants for that MySQL Major Release. Since you only did a minor upgrade (5.1.30 -> 5.1.47) the mysql_upgrade was needless. The grant tables for the Slave have no bearing on Replication since the Slave has to authenticate back at the Master.
Fixing MySQL Replication is just a case of repointing replication from the last know executable position and starting from there. Here is how you do this:
Run SHOW SLAVE STATUS\G and choose the following two fields
mysql> show slave status\G *************************** 1. row *************************** Slave_IO_State: Waiting for master to send event Master_Host: 10.48.20.253 Master_User: replicant Master_Port: 3306 Connect_Retry: 60 Master_Log_File: mysql-bin.000504 Read_Master_Log_Pos: 326579313 Relay_Log_File: relay-bin.081210 Relay_Log_Pos: 326579450 Relay_Master_Log_File: mysql-bin.000504 <--- Choose This Slave_IO_Running: Yes 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: 326579313 <--- Choose That Relay_Log_Space: 326579450 Until_Condition: None Until_Log_File: Until_Log_Pos: 0 Master_SSL_Allowed: No Master_SSL_CA_File: Master_SSL_CA_Path: Master_SSL_Cert: Master_SSL_Cipher: Master_SSL_Key: Seconds_Behind_Master: 0 1 row in set (0.00 sec)
From the above display, your would choose mysql-bin.000504 and 326579450.
Simply do the following on the Slave
STOP SLAVE; CHANGE MASTER TO master_log_file='mysql-bin.000504',master_log_pos=326579450; START SLAVE;
Give it a Try !!!
