In the course of registration, Match.com asked for my email address. When I entered it, I was told that that email address could not be used to register (no reason given); enter another email address.

That is the only email address I have. And I had entered it correctly.

Any idea what their problem is? Any suggestions?

I am not sure what your problem is. You could get another email address, in fact it is probably a good idea to do so. I have a separate email address I use for all 3 of my dating site memberships. This way if I want to dispose of it because some guy is pestering me or something I can.

Try Gmail or Hotmail or even Facebook for a secondary email account.

Hope that helps