I created a sequence on Harmony ONe
I suppose so that you've got at least one software that is able to deal with your remote. Since the issue isn't related to MPTray (you've been able to launch MP using WIN+ALT+ENTER shortcut), I can't help you. Unfortunately, I don't have such a remote and I've no idea which softwares you're using on your computer.
However, you could find some help on the remotes forums. Good luck!