The Fax modem installed on your printer does not appear to be responding with the printer. DSS and WebJet use SNMP to communicate with the printer over the network. Although it appears to be functional management of the fax features from DSS appears to be disabled.
I would consider stopping by this printer and re-installing the fax modem. Perhaps something wiggled loose or there is a failed connection somewhere that is easily repairable. I would assume that if you stopped by the printer you may not be able to configure it from faxing via the control panel either.
Another quick test would be to try and disable DSS temporarily and then configure the faxing feature via the Embedded Web Server. If EWS is successful at communicating with the fax modem then there may be some kind of an incompatiblity issue with that printer and DSS. In that case consider updating firmware and then contacting HPs DSS support area to see if they have any other suggestions. DSS doesnt get much development love so your response may not be satisfactory but its worth a shot to see what they say.