admin page not found on changing htaccess.txt to .htaccess

Hi,
I have enabled seo url in settings and renamed file .htaccess.txt to .htaccess. but after doing it our site works fine, but when i try to login into admin page. it shows admin page not found,

Again after renaming file .htaccess to .htaccess.txt i am able to login into admin panel.

my site is installed in root directory, so pls help me to solve this problem.+

my site url is www.zhatka.com

Regards,
Pravin,

I am able to access the admin login page okay?

I just tried to get to your site and got an Internal Server Error.