Premiere Elements, particularly prior to version 12, is not backward compatible. You can not open a version 9 project in version 10.
In fact, opening a version 9 project in version 10 can corrupt file so that you can't open again later in version 9.
In by books I highly recommend finishing any project in the version it was created. Trying to open the project in a later version of the program can lead to a lot of problematic behavior.
Thanks so much for this very illuminating piece of information. Is there some reason Adobe never warned users about this little issue? For what it's worth, the title problem seems to be the only problem I've encountered as yet. I'm reluctant to get rid of version 10 and re-install 9. Not even sure if that's possible. Sheesh, what a mess.
Well, for what it's worth, that's why I write my books. Available on Amazon.