/%postname%/ does not work

Out of nowhere my site got this error.

If I use this anything with %postname% it does not appear. Something like that:

http://www.site.com/%year%/%monthnum%/%postname%/

All the posts will be:

http://www.site.com/2010/03/

The postname is not working, it does not appear. What happening? 🙁

Everything is ok on .htaccess file. The system can write on it.

Thanks