How to change “permalink” structure in “WordPress Thesis” theme?

I have installed Thesis theme. The default permalink structure is
BLOGURL/%postid%/

When I change it to BLOGURL/%postname%/, I can’t access the pages.

I have modified .htaccess file and the “nav_bar function” as well.

Can somebody help me out? I can’t figure out the redirection error.

first set it to default url & see whether eveything is right, then delete all text in .htaccess & add the new url format you need & save & get .htaccess updated & see your site