pt-table-sync error: Called not_in_left in state 0

Question

I have setup a Mysql replication between 2 servers, using Percona Xtrabackup:

Master is a MySQL 5.0.91 Community Edition (CentOS 4.8)

Slave is a MySQL 5.1.68 Community Edition (CentOS 6.4)

When starting the slave, some replication queries where blocked because of some unknown "temp" tables. I used a few SQL_SLAVE_SKIP_COUNTER commands to hide the problem. And now that the replication is up to date, I try to resync the tables. => 2 tables are out of sync. I use pt-table-sync to resync.

The first table has been resynced without any problem (a few UPDATE to replay)

But the second table, a huge table (57GB), give me this error after some time (varying from a few minutes to a few hours):

pt-table-sync --verbose --execute -uroot -p h=10.2.0.1,D=MYDB,t=MyTable h=10.2.0.2

# DELETE REPLACE INSERT UPDATE ALGORITHM START    END      EXIT DATABASE.TABLE
Called not_in_left in state 0 at /usr/bin/pt-table-sync line 5500.  while doing MYDB.MyTable on 10.2.0.2
#      0       0      0      0 0         16:38:24 19:08:17 1    MYDB.MyTable

Note that I launch pt-table-sync from a third server on the local network.

I don't find much information about this error. What would you recommand to help me solve this problem?