I've used FC2Fix to clean up my expressions and it has worked like a charm. I tried it today and it doesn't work. It loads just fine and the interface behaves like it should, but nothing gets changed. This is the first time I've used it with Windows 10, so perhaps that's the problem. It's a standalone executable, so the version of Poser shouldn't matter. It's written by Gary Sayers, if that helps.

Alternatively, is there another way to "clean up" expressions? Let me explain what I mean by "clean up" an expression. When you save an expression with Poser, it not only saves the expression morphs (smile, eyebrow up, etc.) but it also saves the face morphs (George, Old, BrowHeavy, etc.) as well, so when you try to reuse the .fc2 file later on it tends to set the face back to the V4 default. FC2Fix.exe simply removes the non-expression morphs from the file.

You may have to give the program appropriate permissions to access the files and rewrite them. I don't know how to do that in Windows 10, but if you can right-click on the exe, you should be able to find an option to allow that program to run in Administrator mode, or the equivalent. However, it's important to note that programs that alter external files often need to have the "Always run in Administrator mode", instead of just the "run-once" option for running in Administrator mode for that one execution of the program. So, it'd probably be best to give it permanent access, if that's possible.

Ah, I figured it out. It writes the fixed files to a new folder called FIX. There's nothing that tells you that it does that, but now I remember going through that process before.