[Graeme]

You may be missing some files in your installation….?

My preferred technique for installing is to upload the zip/tarball to the server and then use either command line (i.e. ssh) or a web file manager on my webhost to extract the zip/tarball.

If you extract the zip/tarball on your own computer and then use FTP to upload the bbPress directory tree then sometimes the FTP client can miss some files if it gets interrupted.