So, I believe I know what the problem is, and have a solution (thanks to your replies to my post). All saved X1 MIDI projects give the MIDI port error, which can easily be resolved by either (1) reassigning in the popup window that appears when the project is opened, or (2) by reassigning each MIDI track to the correct output. After correcting individual tracks and saving the project, reopening does not produce the error.
Also, I was fooled by my own default settings that I use for making a new project. My 'default' setting when making a new project results in the reassignment error; however, creating a new project with the 'normal' settings that shipped with X1 does not. And, MIDI played just fine with the 'normal'-made new project.
So, I think I know what needs to be done to correct the reassign ports problem: edit my "default" settings when making a new project to reflect the new output port, and when opening previously made projects, go thru and change the MIDI output port on each MIDI instrument. I'm 90% sure this will work.
Again, thank you for your time and efforts in helping with my problem. I appreciate your good will and assistance.
PS: I will update my profile to reflect my equipment. Sorry about that, but this is the first time I've been on the 'new' forum. My bad...
Bob