You have to define the limit for the binddn you use in your syncrepl
definition ( 'cn=user,ou=login,cn=system' here), or change this binddn
to be the one for which you have an unlimited sizeLimit.

Thanks for the advice Emmanuel.

I finally put these lines on the global limits :
sizelimit size.soft=unlimited size.hard=1000
timelimit time.soft=unlimited time.hard=5

Tell me if i'm wrong but the hard limit is the absolute time /size the server will spend processing the request.