ajax javascripts not working correctly with .htaccess mod_rewrite

Question

The ajax div is showing error in place of loading div. When trying http://mysite.com/a1/just-testing the div shows:

The requested URL /a1/text_random.php was not found on this server.

I am using this .htaccess mod_rewrite

RewriteEngine on
RewriteBase / 

RewriteRule ^a([A-Za-z0-9\-_/]*)/([A-Za-z0-9\-_/]*)$ /index.php?item=$1 [L,NC]