If the program has stopped supporting your form of TIFF, that is not a bug; the company has simply stopped supporting that format. It would have been a conscious decision and is probably related to the program's move from 32-bit to 64-bit, which happened with v25.

I am sorry that this causes you trouble, but I doubt the folks at MM are going to change this. You can certainly propose it as a Feature Request.

As a long time user (since version 2.2) I have created literally thousands of files, at least hundreds containing .tiff files.
As a user who wants to use the software for opening all files created I see it different way:
1. I do not have any problem to change.tiff file for.jpeg or whatever file. 
2. The software has to offer me the option to do it without have to use another (older) version, especially if the support for.tiff files was stopped by Makemusic.
3. If the software which was designed to have a backward compatibility stops responding while opening an older file without giving any option to change and continue to work on it, I insist on what I said: this is a behavior which I call simply a bug.

Juraj, I am not aware of this being an issue or that we have changed the type of TIFF files that can or cannot be used in Finale. I looked through your case with us on this subject, and it did not appear that this was completely resolved nor was the issue you are experiencing replicable. If you would like, please feel free to submit a case with us again and I would be happy to find out what exactly is happening here and what we can do to find a fix for you. It sure would be a waste to not be able to use all of those old files you have.

Hello David,
I will submit the case again and send some file(s), so you or anybody from the support team can check and solve the problem.

Was the file created on the Mac where you’re trying to open it? I’m guessing not. This may be a privileges issue.

Attach a problem file to emai and send it to yourself. See if you can open the attachment. 

Post what happens.