I'm experiencing the same problems on 1 of the two sites I have a test version of roster 2.0 running on.
Since they should be running of the same codebase (the 2nd site is basically a copy) I'm suspecting this may be something server related. I'm going to verify if all the files are equal and let you know if I find something.
edit:
Did a roster diag on the sites and they were identical. The server with the problem has open basedir enabled though.