There is a bug in NNTP version 1.5.10, such that when multiple requests are sent to the NNTP server, the server only handles the first one before blocking waiting for more input which never comes. NNTP version 1.5.11 claims to fix this.
You can work around the bug inside Emacs like this:
(setq nntp-maximum-request 1)
You can find out what version of NNTP your news server is running by telnetting to the NNTP port (usually 119) on the news server machine (i.e., telnet server-machine 119). The server should give its version number in the welcome message. Type quit to get out.