I have made a big mistake...
I was using newbb2 rc1, when upgrading to newbb2 rc3, I ran newbb2rc2_to_newbb2.php. I know it should be newbb2rc1_to_newbb2.php

After upgrading, everything works fine without problem except viewing attachment. files are actually uploaded to right path, but nothing happens when view a topic.

Does this problem come out with my previous wrong updating action? any suggestion to resolve it?

Many thanks.