I have rather disturbing news for you.
You cannot do MySQL Replication from a New Master to an Old Slave
I have written many posts about this:
Nov 26, 2012: Replicate MySQL 5.0 Master to 5.5 Slave?Feb 08, 2012: will replication from 5.5.20 to 5.0.XX server work?Dec 22, 2011: What does the base64 BINLOG statements in mysqlbinlog output mean?Feb 04, 2011: MySQL master binlog corruption
Since there is nothing in the meantime you can do, please upgrade your Slave to MySQL 5.5