There is a definite problem with rebuilding and Norton Internet Security (NIS).
I have had the same problem with the rebuild phase just hanging.
I am running NIS on a PC, on dial-up.
If I disable NIS the rebuild happens without a problem.
I have tried other fixes, such as resetting firewall rules, but that doesn't seem to work, the only thing that I have found that definately does is temporarily disabling NIS, clicking on rebuild, and then enabling NIS as soon as the rebuild finishes. Not ideal I know, but it works.
Have emailed symantec about the problem and will post response if I get one.
Tonto