playing 1 line of music for a quick import into finale.   using a piano.  Sonar and the midi file have double stems...  each note has a stem going up and a stem going down.  never seen anything like it...    And never fails when you need it done yesterday!
 
Sorry..  I place an image and it screwed things up big time...     s o  try this..    imagine a note head is hear  ><
one stem attached to each note ( mostly 1/6 notes goes    UP  ( no up arrow )..  and on the other side of the same note there is a stem going down.
 
When I save this as a midi file ( it was played as a midi line )   Finale looks at those two stems and makes 2 notes:... a 1/16 note and another note head with no stem which looks like S&^T.     The thought of editing every single note head out or stem out is beyond comprehension.     I obviously don't use producer as much as i should or i might have run into this before.   Any clue?
 

Two notes of the same pitch at the same tick.
 
For an image to show it must be a link to a URL for an image on a internet web server.

I played one note only... no sustain pedal...  i wonder if something in the Yamaha clavnova "output" had anything to do with it...   grand piano.
 
I appreciate your thinking of the obvious...  for some people that might not be far off.

Look at the MIDI in PRV to see if the note was doubled as Wookie said. You can use the Deglitch process (in the Global Process menu) to remove a lot of accidental triggers all at once if you find a lot of these in a clip. However it sounds like only one so just deleting the doubled note should remove it from the Staff View.
 
Not sure why staff view would show them at the same spot but it does tend to be a little weird.
 

FWIW...    I outfoxed Finale...  I imported tracks as staffs...   this is interesting...   tracks 0-1 gave me a staff and track  0-4 gave me a staff.
 
Delete one staff and done.
 
Figure out cause later!

Oh... sorry. I read that as being 1 note affected but it is ALL of them? Well again I would check the MIDI clip in PRV to see what's up. With he Deglitch process if the doubled notes are under a certain length, velocity or one other parameter that I forget right now you can set the Deglitch resolution to just above one of those paramaters and it will remove all the unwanted notes.
 
Worth looking into anyway. Not sure what would cause this but maybe the track was being fed by two signals at once? Like doubled channel/port or whatever. I don't know enough abotu MIDI concoct a theory as to teh exact reason.
 
It could, as you said, be something goign on with the patch.
 

Did you right click on the note and then move the pitch up a couple of steps?  That would show what (if anything) is under it.  EX: If you right click and it says C4, just click up to D4 (or right click once to shift it up to C5).  You can always Ctrl-Z afterwards.