The DLP-D dongle or USB-485 cannot be found on a computer, even though windows device manager shows good drivers loaded for each.

Cause:

Another program has accessed the serial ports and has not let them go, thus another program cannot use them.

Solution:

Any suspicious programs must be disabled from using the serial ports.

In this instance, Nokia PC Suite was scanning ports, and it has a setting for not running on startup, this must be used.
There is a dialog box for selecting which ports to scan, but changes here seemed to have no effect.

Other programs along this line was a UPS software which was looking for serial ports to determine a connection to a UPS unit.