Firewall Error

BM 3.8, NW 6.5 sp4
Pretty regularly we get the following error message from 1 website:

Your request is not being processed

ERROR: Your firewall is not properly transmitting the original header for
this request.
IP: (public IP of my BM server)


This is only happening on 1 site, it happens to be our website (hosted
externally). Suggestions?