Custom field search url problem

Hi I am usuing wp3.0 ,
I have a page with slug /medical-center/
and url is like http://mydomain.com/medical-center/
This is a custom page template where a query_post ruining

query_posts(‘meta_key=custom_key&meta_value=’.$s.’&showposts=2&paged=’ . $paged);

So in that page the result are showing correctly,
And in header.php I make a link to the search url with query string like
$output .= ‘‘. $value . ‘‘;
print $output;

Now this is absolutely ok in my local Xampp server,
but when I upload it to my host-gator server it produce a 404 page especially when URLs like http://mydomain.com/medical-center/?s=Abcd

Any help plz..