I keep getting a problem whereby the links in the quick nav bar are not found :-

Not Found
The requested URL /concrete5/dashboard/system/ was not found on this server.

This happens to all the links, including the full site map, dashboard, system and settings etc
I have not made any changes to the file system structure or altered any permissions.
Here is the directory listing on my server, which is Debian 6 (Squeeze).

dave@www:/usr/share/concrete5/files$ ls
1113 3413 6213 8413 avatars cache index.html tmp
2813 4713 6613 9313 backups incoming thumbnails trash

I would appreciate some help, please..