You have to extract the .po before you can use the translations. First, open /b2evolution/blogs/conf/_locales.php in your favorite editor, and make sure that

$allow_po_extraction = 1;

is set. Then go to http://www.yourdomain.com/path/to/b2evolution/blogs/locales/ in your favorite browser, and click the [extract] button to the right of your locale.
Then test it a little, and if you feel comfortable with the additions, you can mail it to either me (click the "mail" button below my post) or Francois (use the mail address you find [url=http://fplanque.net/About/index.html]here[/url]), and we'll look at it and add it to the next release. :)

-Vegar

Thanks for your reply. Unfortunately, I'm still unable to solve the problem. My path is www.ex-post.org. I go to http://www.ex-post.org/locales. I then generate the string by clicking on 'extract'. After doing so, I receive a long error message that begins:

Warning: fopen(es_ES/_global.php): failed to open stream: Permission denied in /www/docs/ex-post.org/public_html/locales/posplit.php on line 125

Warning: fwrite(): supplied argument is not a valid stream resource in /www/docs/ex-post.org/public_html/locales/posplit.php on line 126

Warning: fwrite(): supplied argument is not a valid stream resource in /www/docs/ex-post.org/public_html/locales/posplit.php on line 127

[etc.]

Regards,

Pablo