So I search in this forum and don't find solution. Then i search in google and found a fix in an old wp forum :Warning: gethostbyaddr() [function.gethostbyaddr]: Address is not a valid IPv4 or IPv6
find : gethostbyaddr and replace by @gethostbyaddr. So in Statistics.module.php line 274 i replace that and it seem to fix the problem : the warning message disappear.
I don't knows if it is the good solution and i don't know exactly what i do but it works for me...
Anyway, many thanks to the author of this module.