I found this in the manual:

Error 052: Broker interface busy


The used Zorro version or broker plugin did not support multiple trading instances (see restrictions). Zorro attempted to log in to the broker, but another Zorro instance on the same PC is already connected.

but I don't see anything about where to get the "multiple instance broker interface". Is that something I can do with the non-S Zorro version, or do I get it from FXCM?