Not for sure if this has anything to do with your problem, as I couldn't find anything on the "Error 501, Bad Command Usuage" but did find this:
"Error Bad Command Usage is that the computer's network name or description is configured to an invalid or illegal name." What ever that means?
And also with Usenetserver had this on their front page and might also be a cause of the problem, but not for sure:
Wed, 28 Nov 2007 22:22:55 GMT
We have resolved the connection issues with news.usenetserver.com and you should no longer be receiving 400 errors.
The reposted statement below is still valid for SSL. According to tracking information that we received today, the new hardware should arrive tomorrow. Our plan is to get the new hardware racked up and in production by Friday evening. We apologize for the delay.
***** REPOST *****
Due to the overwhelming popularity for SSL connections, we have seen a sharp increase with connection requests over the last few weeks. Subsequently, we will be requiring additional hardware to handle the increased demand. The new hardware has been ordered and will arrive in a few days. Until we can get the hardware in production; you may receive connection errors while attempting to make a connection to our secure server, secure.usenetserver.com. You can connect to our non SSL servers by using news.usenetserver.com in the mean time. We apologize for the inconvenience this may cause you.
***** END REPOST *****
Maybe after they get all the bugs out of the hardware installation, you might not see this again...