jdMorgan - 8:12 pm on Apr 25, 2011 (gmt 0)
Delete your browser cache and try again. Forcing a page reload is not enough... Delete the cache.
Although you may get this code to work, be aware that you are committing SEO suicide by using it. Re-read g1smd's comments above. You must modify the WP configuration or the script itself to produce the correct URLs. This is *required* if you want to avoid disastrous damage to the ranking of your site in search engines.
Given a choice, I would leave your wp-admin URLs alone and forget this whole project, rather than using the "bad solution" discussed in this thread. The redirect code may very well work, but it is not what you want to do if you care about your site's search ranking at all. Each of your pages must link to correct URLs, and there is no "redirect-based quick fix" for that.