I have exactly the same symptoms so it doesn't seem to be your environment exactly. (I'm on Xp Pro with MySQL)
Can anyone help us?
I have the same problem and I posted my questions two weeks ago, Still I did not get any answers.
Was there an error message display on the console? Or in the log file? The error text posted so far doesn't give me much to work with. I have run 2.4.0 with MySQL and PostgresSQL in XP and FC5 without seeing this error. I have seen some "error" messages show up on the console, I think they were JSF-related; I just ignored them and the Management Portlet displayed just fine.