Can I assume that you are using WHS2011 as you have posted in this forum? The reason I ask, is that I was not aware that Asus made a server with WHS on it. Anyway, back to your problem - try running ShieldsUp at www.grc.com and confirm that the following
ports are open:
WHS: 80, 443 & 4215
WHS 2011: 443 (& optionally 80).
Phil P.S. If you find my comment helpful or if it answers your question, please mark it as such.