[mossyuk]

I think your DIR path should point to the 'virtual' path - relative to your web site root, rather than your physical disk location.

My CH_DIR path points to /vb303/

as an example, my 'root' web dire looks like:

vbindex.php
vbiconfig.php
vb303 (DIR - the 'forums' DIR that vb3 rc3 comes in, but renamed as im running a test site)

define('CHDIR_PATH', 'vb303');

other examples would be like ../vb303 ./vb303 /vb303 /my/path/to/vb303 etc etc

Hope that helps!