Adjust the host file or network traffic to pair the servers so that one server will always initiate and respond to requests to the other paired server:

NCWEB1 < - > CRMWEB1
NCWEB2 < - > CRMWEB2
NCWEB3 < - > CRMWEB3

When a transaction download is started from a CRM server, a call is made to the NetCommunity or BBIS web server.  That call has return information that needs to be routed to the initiating server.  If this can't be done with in-place network hardware, the host file can be adjusted at each server to always resolve the server names to specific IPs.  If the routing isn't set in this way, the error described in this solution is the result.