I'm trying to trade a simple futures strategy via Interactive Brokers. I get an error from the IB side:

Error validating request:-'bm' : cause - Please enter a local symbol or an expiry

I've been on the line with IB tech support and they say that the only way this error can arise is due to a contract misspecification on my side. IB told me that these are the strings that correspond to the parts of their API's 'contract' object:
Symbol = ES, SecType = FUT, Expiry 201703, Exchange = GLOBEX, Currency = USD

I can confirm that entring ES-FUT-201703-ESH7 in the 'Symbol' column of my AssetsFix.csv file (which is how I interpret the futures example in the Zorro manual), I get the error described above. This results in a 'Error 53: ES-FUT-201703-ESH7 unavailable at this time' on the Zorro side.

I have also tried using all the combinations of Symbol-LocalSymbol-Expiry-FUT-Exchange-Currency that I could think of, but the error persists, including the full contract expiry date (20170317).

Also confirming that I do have this data subscribed and active in my IB TWS and my account is permissioned for US futures.

Could this be a bug in the IB bridge or am I doing something obviously wrong?