Last month I posted about DirecWay problems with MarsEdit. It occurred to me today that the problem may instead lie with the way DirecWay does "Web Acceleration" and that it could be interfering with the XML-RPC calls.
A quick search reveals that this indeed seems to be Direcway XML-RPC problem. The author of the WordPress article suggests it is related to latency. I'm not certain as it was working for me at one point over the satellite connection. I noticed, however, a problem with DirecWay's cache last night. At one point it attempted to load this site and munged the .css files associated with it. From then the only way I could load the site was to power-cycle the DirecWay box and load it before the Web Acceleration kicked in.
So I called Ground Control tech support and they say there is nothing that can be done. They recommend contacting the author of the software to have the problem with their system fixed.