MIDI errors (PSR-GX76 + Midisport Uno)

Hello,
I'm new to Home Studio, and I am running into trouble trying to connect a MIDI keyboard. I'm working with a Yamaha PSR-GX76 and a M-Audio Midisport Uno USB interface.

With everything plugged in and HS running, pressing a single key results in wrong notes that cut in and out, almost as if I were exceeding the polyphonic limit of the keyboard. With non-sustained voices such as piano, there is sustained reverb from a lower-register note that hasn't been pressed. With sustained voices like trumpet, 'note off' messages are non-existant for both notes played as well as some that aren't. Basically, the notes don't shut off after releasing the key.

At first, I thought this was the soundcard. I was using one that came with the mother board, so I replaced it with an SoundBlaster Audigy 4. The original latency was resolved, but the note symptoms described above remained. The driver is current.

From reading other posts, I realize that turning local control off on the keyboard is important. However, following the instructions in the PSR-GX76 manual didn't seem to do anything. (I am assuming that with local control disabled, no sound is produced from the keyboard's speakers, unless sent from the sequencer.) Upon closer inspection, the manual that came on the disk with the keyboard omits any mention of local control - I was only able to find instructions from the Yamaha support site. This makes me wonder if my keyboard is an earlier release - one without local control toggle.

Among other things, I have tried disabling midi echo from within HS. I also have the 'local off' parameter enabled on startup. I have even tried unplugging the connector from the MIDI-IN jack on the keyboard and leaving the MIDI-OUT intact. None of these changes had any effect.

I tried using a different MIDI program (a simple one that came bundled with the keyboard) and I got the same garbled results, so I'm pretty confident that my problem is with the keyboard or with the interface.

The interface seems to be working - I updated the driver and tested the MIDI-OUT path by playing MIDI files through the keyboard from windows media player. It worked fine, but I did notice that the LED indicator light for MIDI-OUT behaves differently than the MIDI-IN light. With messages going out of the interface, the LED flickers in response to silence vs. sound. The MIDI-IN LED stays constantly lit as soon as the keyboard is connected and powered on. The M-Audio site says this is not an error - I thought I would include the info in case there are any other Midisport Uno users with different experiences.

So, that's where I am right now. At the moment, I'm looking into borrowing a MIDI keyboard from someone else so I can isolate the problem once and for all. If anyone can see steps that I've missed along the way, I would very much appreciate any tips or hints you can offer.

Thank you.