https://usermanuals.finalemusic.com/FinaleWin/Content/Finale/Speedy_Entry.htm?Highlight=Speedy%20entry 

Insert Notes or Rests. Choose this command to insert the note or rest to the left of the cursor. If Use MIDI Device for Input is selected and you are holding down a key on your MIDI keyboard, you will insert a note. Otherwise, you will insert a rest.

What if you do not have a keyboard in your office all the time (it is very small).  For 20 years , if you use a number pad, the default was always a note, and one tap on the "back space" button and it would flip to a rest. After using both for a while (many, many years ago) I actually found it was faster with number pad entry, so that is what became my entry method of choice. Why would Finale switch to a rest being the default.  Aren't most inputs in scores and parts notes not rests?  To switch it around would be kind of "stupid" wouldn't it?

Make sure Use MIDI Device for Input is NOT checked.

Are you using Simple or Speedy? I use Simple with the QWERTY keyboard and numberpad, and enter the notes with the letter keys, and the rests with numberpad 0 (zero.)

I am adding a third part to Flute duets that I have already written. I have had success with some of them, but others with ALL of the same settings will not accept speedy entry even though ALL settings match the previous arrangements that are successful. Some of them that I have already added the third part successfully, will or won't play back with no differences in setup from others that do. I don't know why.

Device setup and all of the other settings match the successful ones. Either I cannot get Finale to recognize the MIDI input and thus get rests, or I can not get any play back with VST as on the successful arrangements.

I have been using Finale for 25 years, and am pretty good with problems, but this stumps me.

I am using PC, with Focusrite MIDI interface. Everything works on some of the work, but others with EXACTLY the same settings will not. I have sometimes gotten the message can't open device twice. I will shut down and restart and sometimes this will work. But even now that is sporatic. I am using  version 2014.5 usually with Garritan personal orch 5. (Piano or Flute sounds). Speedy entry for me will not sound at all unless I use VST output. If the problem was not sporadic I'm sure that I could solve the problem? Please help if you can.  Jack, the Quiet Bear

Which computer operating system are you using (including which version)?

I am guessing you have checked that MIDI cables are firmly plugged in at both ends. How old is the Focusrite interface? I recently had to replace my older Yamaha unit with a new interface after (decades?) of use.

… but others with ALL of the same settings will not accept speedy entry even though ALL settings match the previous arrangements that are successful. … I cannot get Finale to recognize the MIDI input and thus get rests …

In this particular case I would take a look in the Speedy menu:

Is the menu item “Use MIDI Device for Input” selected or de-selected?

… Some of them that I have already added the third part successfully, will or won't play back with no differences in setup from others that do. … I can not get any play back with VST as on the successful arrangements …

Take a look in the MIDI/Audio menu.

Is “Play Finale through MIDI” perhaps selected? (this could be the culprit)