I’ve just spent a few hours frustrated with the same problem, getting errors 66 and 67 when using the “net use” command. Happily, I found a solution! From geekswithblogs.net, I discovered that the Norton Firewall was to blame. Here are the instructions I followed to get printing to work to the USB port:
Most personal firewalls will block printer sharing. You need to allow for printer sharing over 127.0.0.1. For Norton Personal Firewall (part of Norton Internet Security), open the configuration window for the firewall. In the “Networking” tab, first choose the proper settings (Home, Away, Office, or Default). Click the “Trusted” tab below, then “Add…”. In the window that comes up, make sure “Individually” is selected, and enter “127.0.0.1” as the host to allow. Click “OK” in this window, and “OK” again to leave the Firewall configuration. If you want to allow sharing under different locations, change “Settings for:” in the pull-down menu to and repeat the steps to add 127.0.0.1 as a trusted host. I was getting “system error 66” when trying the “net use lpt1 …” command until I completed this step.
Other firewalls probably have similar settings to change.