Problem with .htaccess

Not sure if this is the right place to ask this question. I have a WordPress installation that is working fine. In another subdirectory I have another WordPress installation which also is working fine. This is available as a sub domain (sub.mydomain.com).

I have created another a subdirectory (www.mydomain.com/sub1) where I have installed a lifestreaming application. When I try to access that directory I get a 500 error. I have also tried to make it a sub domain both still get a 500 error.

The contents of my .htaccess file is as follows

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

Do I need to modify anything in this file to allow me to access http://www.mydomain.com/sub1?

Kind regards
Gustaf