I have installed a wordpress on my server running on apache2. After wordpress installation I tried to change the permalink setup to

/%year%/%monthnum%/%day%/%postname%/

After the change pages are showing following error

Not Found

The requested URL /2011/03/14/hello-world/ was not found on this server.

Apache/2.2.9 (Debian) PHP/5.2.6-1+lenny9 with Suhosin-Patch mod_python/3.3.1 Python/2.5.2 mod_perl/2.0.4 Perl/v5.10.0 Server at <addressremoved>.com Port 80

Please help me