This is a generic Mac OS error. Usually it means that you cannot write to whatever directory the file is residing in. Often, you will get it if the file is on a remote or USB drive and you have Read Only privileges instead of Read & Write. It can also be caused by corrupt preferences.

It can also be caused in some applications if you created the file on another computer and did not zip it before moving it to yours. Word is notorious for this but I can't say I encounter it with Finale.

Move the file to a new location. It will probably copy. See if you can now open, write to it and Save.

You may also want to export the file as XML as an emergency backup before trying to save it if you are still having problems.

I am seeing the same error, and it's not dependent on the location where I'm trying to save the files:

* Finale files -- where all my other .mus files are

* Documents

* Desktop

This is aggravating. I'm on a Mac. The file was created on Windows by someone else in the group; I've extracted a part and made a truckload of modifications. Why does this not work? 

What version of a Finale are you using? What Mac OS? What version created the original file?

Finale version says 25.0.0.7722.

MacOS 10.12.4. 

Version that created the original file: I don't know the precise version, but I think it's one release down from this; I waited for the version that was supposed to be backwards-compatible before upgrading. 

First, download the latest version, 25.3.... I don't know if that will help but you are 3 builds behind.

The last version, like 25, creates .musx files, not .mus.  But you were able to open it.

You cannot save to the original file when you are working in a newer version. Before anyone corrects me, you can export to .mus that can be opened in 2012 or to MusicXML to be opened by many older versions but you cannot work on an older .mus file and save back to that file. In addition, if it the source is not a file that's part of your Mac, it is unlikely that you would have privileges to write to that file, anyway. There are ways but you have not given enough information for me to do anything but make an educated guess—it's still a guess.

Finale should have prompted you to Save As and make a copy (make sure you save it to your Mac, not a remote shared drive or DropBox). That will be a .musx file for which you will have admin privileges and full permissions. Your problem could be that simple. When you're done, you can upload or email it to wherever it is to go.

Also see if any of this applies:

https://makemusic.zendesk.com/hc/en-us/community/posts/115006458687-Can-t-save-file-if-left-open-for-a-while-?page=1#community_comment_115003869328

I just had the same problem. I also used to have this problem with finale 2012, and hoped that upgrading to 25 would solve it, but it didn't.

Anyway, a trick I just used worked: Open another finale file (let's call it file B), copy & paste the section I just worked on file A that

couldn't be saved to file B and save file B. Close both files, quit Finale. Reopen both files and copy the section from file B back to file A.

The problem seems to pop up when leaving Finale on for too long, with my computer went to sleep and back on. Saw another thread saying this can be prevented by creating a "Finale Temporary" folder and going to Finale/Preferences/Folders and check Temp Files and choose the new "Finale Temporary" folder, then going to Save on the left and choose autosave every 15 minutes and make backups when saving files.