.htacces is not working with CI 1.7.3, php 5.3 and ubuntu 12.04

[eluser]sonu gautam[/eluser]
Hi All,

I tried to hide the index.php with .htaccess, CI 1.7.3 and php 5.3 and got an error 404.
But it's working fine on my development server which is having php 5.2 and rest of all are the same configuration, i developed my application with HMVC and my .htaccess is

Code:

RewriteEngine on
Options -Indexes
RewriteBase /myapp/

RewriteCond %{REQUEST_URI} !(\.[a-zA-Z0-9]{1,5})$
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ /myapp/index.php?/$1 [L]

Anybody suggest me the way how can i resolve this issue should i upgrade my CI version ?

Thanks and best regards

Sonu Gautam