Permalink Setting

Hi All –

Trying to change my permalink settings to reflect the post-name only. Yet, every time I change it, it gives me an error when I click on the actual link.

blog is @ http://blog.yourpersonalsuccesssolution.com/Success-Solution/

Given that, what would I input into the custom structure box?

Question: If I change the permalinks after I already have posts, will it also change the permalinks on those posts or only the ones thereafter?