Changing permalinks

I am trying to change my permalinks to the “date and name based” format, and change the category permalinks, from the default setting.

When I click “update permalink structure” nothing happens. It does say “Permalink structure updated.” but the little dot by “Default” is automatically filled in again.

I have tried clearing the cache, and disabling the cache, and my .htaccess file is writable. I am using semiologic pro theme.

Any advice? Thanks in advance..