This very situation happened to me twice when I was getting interviews lined up. The first time it happened I sent a second email after a couple days of hearing nothing, and when I still got no reply I called the coordinator. Turns out she never received any of my emails, and she told me she'd had similar problems from others, but this seemed to go away if people REPLIED to one of her emails (as opposed to sending her a new email). Dunno what was up with that.
The second time it happened I sent a second email from the initial email address as well as a completely different email address. The coordinator only ever received the email from the different address, so I guess some people just have trouble receiving email from my gmail account. Kinda' weird though because the vast majority of programs had no trouble whatsoever.
Long and short of it, if you don't hear back within a day or two, email again with a different email address or call.