I had this same problem the day that 2.5 was launched.
My problem had to do with certificates and Internet Explorer, as far as I can tell. I normally use Firefox so I had never been to the SL website with IE.
After I launched IE and then logged into SL's website from there once, I was able to load the profiles in the in-world viewer as well.
Caveat: I do not remember if I had to close SL then re-log in order for it to work.
Caveat2: I'm not sure how this will work for a Mac since there is no IE for Mac.