viewvc problem when doing a diff

Hi,

I have subversion 1.3.1 / Apache2 installed and viewvc-1.0.0-rc1 on top 
of them.
Browsing works fine, but when I try to run a diff I get the following error:


     An Exception Has Occurred

Invalid path(s) or revision(s) passed to diff


       HTTP Response Status

400 Bad Request

------------------------------------------------------------------------


       Python Traceback

Traceback (most recent call last):
 File "/usr/local/viewvc-1.0.0-rc1/lib/viewvc.py", line 3609, in main
   request.run_viewvc()
 File "/usr/local/viewvc-1.0.0-rc1/lib/viewvc.py", line 386, in run_viewvc
   self.view_func(self)
 File "/usr/local/viewvc-1.0.0-rc1/lib/viewvc.py", line 2663, in view_diff
   p1, p2, rev1, rev2, sym1, sym2 = setup_diff(request)
 File "/usr/local/viewvc-1.0.0-rc1/lib/viewvc.py", line 2614, in setup_diff
   p2 = _get_diff_path_parts(request, 'p2', rev2, request.pathrev)
 File "/usr/local/viewvc-1.0.0-rc1/lib/viewvc.py", line 2568, in 
_get_diff_path_parts
   'to diff', '400 Bad Request')
ViewVCException: 400 Bad Request: Invalid path(s) or revision(s) passed to diff


Is it something I am supposed to change in viewvc configuration in order to use 
diff ?

Thank you.
Ionut