how use sql_slave_skip_counter to restore slave replication

[AESYS S.p.A. [Enzo Arlati]]

I'm trying to use teh parameter sql_slave_skip_counter at run-time to
restore slave replication.
When a slave replication broke due some errors in code, my be a duplicate
key, the only working way to restore the replica where to delete the
existing record which conflicts whith the ones inserted by the replication
process.
So if I have a duplicate key 30020 ,I have to remove the record with the id
30020 and the replication can reinsert it's copy of record with id = 30020.
This should be difficult to automate so I try another way using the global
variable sql_slave_skip_counter.

I try to skip 5 records using a statemente like this:
set global sql_slave_skip_counter = 5;
and then restart the slavre
start slave;

but the problem is the same and the command 'show slave status' report a
skip_counter filed equals 0.

Where I am wrong , some can help me ?
Regards, Enzo