Dear Xiang-Jun,
Thanks for your quick reply. I do not know how this was only happening to me, but that is exactly what I have tried, using three different browsers. In all cases, the link for all versions led to complaint about forbidden act. At the end, I tried to ssh to my campus linux workstation and it finally works. Do you think this is because my off-campus IP is blocked somehow by your server for downloading? Anyway, this is just for your reference.
Thanks again,
Yuan