Please check the following:
There must be network connection between the PC and server,
Check if you can ping the server from the pc.
Agent PC:
FTP option in USBClient must be enabled,
in the USBClient.ini MUSTFTP=1
Make sure that TCP port 21 is available (this is the ftp port on the agent PC).
Check the firewall settings.
AMETHYST Webadmin:
Check whether FTP scheduling enabled, this must be disabled, FTP must be set 'live'.
AMETHYST Webadmin -> Home Page -> Redirect client to FTP address,
enter IP of AMETHYST server.
Setup FTP times for clients, clear the ftp times to set to live updating = ONLINE.
Now close and re-open USBClient.