So back story I work at a midsized company ie several hundred employees.
Don't sweat it!
Okay i just have to say ARG
I emailed Sunday.
I didn't act on my interest before because I was in a relationship then but still willing to enjoy the scenery.
If this is a guy you hardly interact with at work then I think the usual problems of dating someone at work wouldn't really apply that much.
If you didn't pursue him while you worked with him when you were attracted to him you may want to avoid doing so through E-Harmony.
Do you think he knows it's you that he has contacted through eH? I'm not sure how eH works, if he can see your photo or not.
I'm assuming he doesn't know it's you. I say why not turn it into something playful? I'm thinking you have to go through a bunch of questions to get to open communication, that you can't just write something? In any event, I'd acknowledge that you know who he is and identify yourself and that you had cancelled your membership but now you're back on and saw his email. Make it fun like "Can you believe you work one floor up from me?" or something better than that. I myself would be a bit hesitant to contact him through work, plus you don't know if he's dating someone else right now--you don't want to put him on the spot.
And I won't lecture you about dating at work--I know plenty of people who met through work and it turned out just fine.