I just installed JoomSEF and I am getting the "500 Internal Server Error". I read the Faq, but I still don't understand what is wrong.

Whenever I use any version of .htaccess (including copying the htaccess.txt file to .htaccess), I get the 500 Internal Server Error. However, if I remove the .htaccess file the website works.
SEO Settings for the website are:
Search Engine Friendly URLs: Yes
Use Apache mod_rewrite: Yes

My website is not live currently, and I am using Wampserver 2.0.

Joomla 1.5.15
JoomSEF 3.6.3

Please help,

kelvin

ps - I am attaching the htaccess file last used