I'm having the same problem. Have the latest version, cookies etc. enabled. Have latest MacOS (Lion) and everything I can think of is up to date. Also, the configure link to the external website for Xcite! X4 won't work either. Since it's another link to a website probably the same issue.
My own profile does not work either and I haven't blocked it.
Hope LL fixes this soon. Can get profiles by logging into the website and doing search on the avatars name but that's a pain.