Printers that use ports that do not begin with COM, LPT or USB are not redirected in a remote desktop or terminal services session. To force all ports to be redirected, the filtering type has to be changed. This is done in the registry.
Restart the client, log in to your session, and all ports should be redirected.
You can use other values to set the FilterQueueType to filter in/out other ports:
Starting from RDP 6.0, this setting is no longer valid.