Background story : the master server have a lot of databases. But all of them have a table named 'online' with the same structure.

When I tried to replicate that server to another, the process always fails will error message " Duplicate entry … table online at somedatabase" 

I reset the master several times, and rebuilt the slave multiple times as well – still same problem.

The solution ? 
Excluding the table from being replicated, by putting this line in the slave's /etc/mysql/my.cnf :

replicate-wild-ignore-table = %.online

Restart the slave – voila, master-slave replication works smoothly 🙂

Why ? My guess is something with the table's structure. Because ALL these tables only have 1 record in it :-/ so, what duplicate entry ?? 🙂 #LOL