I'm not sure why you'd be having a problem because I have it installed here:
http://www.e-ztheme.com
...and as you can see, the theme works perfectly fine.
Just out of curiousity, in your forums config:
http://www.yoursitename/modules/Forums/admin/index.php
... under "General Board Settings", are your settings as follows:
- Default Style: subSilver
- Override user style (Replaces users style with the default): NO