First, try restarting the computer

Thank you Mike Rosen, restarting the computer did it.  How many problems can be fixed by just doing that ;)

Glad to help!

Hi,

I restarted my computer. It is not doing undo. This is not good! 

Any other remedies to this serious issues, please?

I just fixed this by going to Finale Preferences> Program Options > Edit > Allow Undo

Mike,

Glad to see you contributing again. We need your PrintMusic expertise among other things.

For example:

https://makemusic.zendesk.com/hc/en-us/community/posts/115000711547-How-do-you-end-a-hymn-score-half-way-through-the-last-measure- 

Thank you Chekad for helping me solve undo problem.

Thank you Chekad! Don't know how that box got unchecked, but that solved it! Why is it even an option to not allow undo's???