This is a simple text file with critical bits of info that I have built up over a long period of time. Fortunately, not long ago I decided the info was so important to me that I needed to copy / paste it into a secure Word file, creating an occasional "snapshot" just in case for some reason it became unavailable to me...go figure.
Strange thing about this is that even though Evernote gave me the error, the error message was transparent and I could see that the file had in fact opened under it, I just couldn't scroll through the file. Once the error message popped up I was forced to acknowledge the error message on top which would then immediately cause Evernote to close and the open file to dissappear.
I finally decided to create a new note, copy the info from my "backup" into the new note, then delete the old note. The old note is now gone, I renamed the new note to match the old one, and the new note works correctly.
Lesson to be learned. NEVER, NEVER, NEVER EVER trust completely any one form of technology with your critical data.