Peter,
I think we've solved the mystery between us, the programmers and I.
At the time Bill and Raymond sent you those emails, the box on your Profile that says 'Allow only fellow Classmates to view my Profile details', was probably unchecked. Checking it makes sure only others registered on the website can see your personal details but, if you leave it unchecked, anyone putting your name into a search engine is likely to come across your Profile and from it they can go through the motions of sending you a message as if they were also registered on the website.
I don't know what dates they sent you the messages but, at some stage after receiving them you (or even I, as I'm in the habit of doing it if I see it hasn't been done)must have checked the Profile Visibility box on your Profile, thus preventing anyone else from doing what they'd done, in future.
Anyone who sends you an email in that way can be replied to, which is what you tried to do. The fact that you couldn't means you don't have a default email program hooked up in Windows. If you click an email link in a web browser your default email program will immediately launch, but only if you have one. This seems to have been why the 'Respond' button, you saw beneath those two emails, failed.
As I'm sure you would liked to have been able to reply to Bill and Raymond, I've asked the programmers if there is some way they can check to see what email addresses the two emails came from. If they come up with them, I'll let you have them and you can send Bill and Raymond an email direct.