Relay log corruption in MySQL
This error marks a corrupted binary log on the slave. There can be many reasons for this. Assuming that master logs are correct, you can simply reset the relay position on slave by:
mysql> stop slave;
mysql> show slave status;
##-- Read values: Relay_Master_Log_File and Exec_Master_Log_Pos<
mysql> CHANGE master TO master_log_file=<Relay_Master_Log_File>, master_log_pos=<Exec_Master_Log_Pos>;
mysql> start slave;