Were you using an UA IP address? Like in the UA Club, were you using one of their computers, or their wireless access? Their wireless access may have an UA identified IP address. When I followed the link in your post, it gave me a screen for logging in as an UA employee. I tried logging in to my MP account from an IP address using a VPN blocking service and had no problem logging into my MP account.
Try using the VPN from your own wireless access.