updates your host/ip in case they have the wrong values.
Are you able to open a dcc-chat window with someone? /dcc chat NICK
Are you able to dcc send a file to someone? /dcc send NICK versions.txt
Were you able to dcc send before?
That tells us whether it's a problem relating with just the fserve, or also with dcc's in general.
If you're sure your router has been set up to make dcc's, make sure you haven't been dynamically given a different ip address than before. ie your ports forwarded to 192.168.1.101 but your ip is now 192.168.1.102