I have two zones for my SP2010 site collection: default (uses Win Auth- claims) and internet (uses FBA to an AD user store). I have a WP which would call the User Profile Web Service and get some profile data back. It was working fine until I changed the default zone's authentication method to allow FBA in addition to Win Auth (claims). Now when I call the USP web service (which is inside an runwithelevatedprivileges block), I get an unauthorized exception.
So, this authentication change seems to have broken my ability to call the UPS web service.