I have a Datasync server set up behind our firewall. It is accessable internally - wireless connection - but not from the WAN. According to the ports list, DS uses 80 and 443 for device access. 4500 is for DS access to the POA and 8120 is the web admin.
I have forwarded ports 80 and 443 (previously only had port 443).

Using a browser for port 80 attempting to access the external address gives the following:
Proxy Error: The proxy server received an invalid response from an upstream server. The proxy could not handle the request GET http://dsync.address/
Reason: Error reading from remote server
Apache Server at dsync.address Port 3128

Does the device require direct access to the server on other ports? Any idea what's with this proxy above? The DS machine has SLES11 + Datasynchronizer only. It is a dedicated Virtual Machine.
Looking at the ports on the DS server open for listening it only has port 443 that seems to be relevant