Thanks! FXCM Australia is apparently a lot more courageous than FXCM Europe.

I've checked their version 604 and from what I can see, the MQL4 language has indeed changed. Some data structures are now different, but this will only be relevant when you do complex things with strings and arrays, or use external DLLs. 90% of existing EAs will probably still work.

The Zorro EA is obviously one of them, at least I can connect Zorro to 604 without problem, and trading also works.

If anyone has a persistent problem with 604 that can't be solved with the suggestions at http://manual.zorro-trader.com/mt4plugin.htm, please post here and I'll look into it.