I've created a trail and did some testing, but it seems that usenet.farm is extremely slow when asking for their newsgroup list and takes almost a minute for the server to response.
Not just from Usenapp, but also if you connect to their server using telnet.
I don't know if they have an issue at the moment or if that is their normal behaviour, but it's not normal.
Anyway, what you can do is to increase the socket timeout setting to 30 seconds or a minute.
You can find this setting in Usenapp->Preferences->Download->Advanced.
I advise you to change this settings back to 10 seconds after you've successfully downloaded the newsgroups list from this provider.
Let me know.