This is doing the trick:

contractUpdate("MES-FOP----CME",0,CALL|PUT|FUTURE);

I get now:

[77: Wed 23-10-11 11:00] 4358.24/4358.24\4358.24/4358.24 -0.0
!Get Future Option Chain MES-FOP--0.00--/--USD
Chain of 7324 MES-FOP----CME contracts

Hope that helps!