If you have a Keyspan USB to Serial convertor and are having trouble getting your system to see the interface connected to it:

Within FreeMIDI:
1) Go to the File Menu -> FreeMIDI Preferences
2) Under the MIDI Configuration side, make sure you have the Keyspan 'Printer Port' and P#### port selected (i.e. checked),
3) Close this window and go to the 'Configuration' Menu -> Update Interfaces
4) Under the Current Interface heading you should have two drop down menus. Set both of them to 'None'.
5) Click on the Scan button for each port, the MTP -should- scan on whichever port you have it connected to.

If the above to does not work for you, check the cables and try hard resetting the piece (usually powering the unit off, holding in the Panic button, power the unit on) and rescan for it. Also, check Keyspan's website for updated drivers.