All it does is tell windows what mail program to launch and supply that launch with the email address and not much else. It's not a great loss when it doesn't work BUT WAIT. Internet Explorer is still the prime infection point for most machines. Why fix this? Use something else.

Q2. Since all I have is "unable to open" I have so little to work with that I have to defer to "Use Windows 7's XP MODE" for that one.

I see not a word about any message, how this was installed or if you tried the various compatibility modes. I didn't write about the compatibility modes since you can research that.
Bob