I had repeated problems during my last stay. Kept trying to log in via the HHonors option (first on the list).

Described it here: http://www.flyertalk.com/forum/25358910-post449.html

I am starting to recognize that Hilton wifi is, like many travel program "benefits," only intended to provide the advertising benefit to the company... and that there is heavy reliance on the bulk of the customers not being able to realize that they are being hosed.