Please be more specific.

1) Windows Finale or Mac Finale?

2) Specify the steps you’ve already taken (to solve the problem), so that we can rule out things.

3)
- Finale has a Preferences file. Have you tried trashing that file? When launched again, Finale will create a fresh, new Preferences file.
- Have you rebooted?

4) - document specific? - or in all Finale documents?

What Peter says. We need a lot more information.

Is the piece that's causing you trouble one that you began from scratch? originally created in Finale or…? downloaded from the internet? one that someone else sent you? imported via MusicXML?

Finale certainly has Undo. There are many options regarding measure numbers—some are required by Broadway style shows to keep track of additions and cuts and if you are looking at one of these scores for the first time, it can be quite confusing.

I know what I am about to say is not received well so please take it in the sprit that it is meant to be. A lot of the "bugs" folks see or complain about in Finale or perhaps many complex programs is not knowing how to use the program. Finale is one that is as easy as you want it to be or as difficult as possible.

This is why the guys and me need exact steps you have taken and computer gear you are using. There are people here that are extremely competent in Finale and computer hardware. Plus they are willing to help but they need info as much as possible.