Getting error when using Pre_get_hook

Hi

I am trying to use pre_get_posts--> basically to detect when a certain type of URL is being loaded by WP- and then run some code, finally redirect.

The function that actually does the background work is named load_zillow_data_before_search

The function that actually detects the URL and runs the above function is named filterpropertysearch

This is the code for the function filterpropertysearch--

function filterpropertysearch($query)
{
$current_url = "http://" . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'];
if (!is_admin() && strstr($current_url, "property-search")) {
// DO YOUR THING HERE, THEN REDIRECT
load_zillow_data_before_search();

}
}

Basically I want that whenever the URL contains the text "property-search" in it then the function load_zillow_data_before_search should be executed.

This is the code linking the function to the action hook of WP--

add_action( 'pre_get_posts', 'filterpropertysearch' );

But when I run my WP site--
take a look at the screenshot-- the URL contains the string I want to detect, yet the above hook is not working. What am I doing wrong here?

The screenshot is here--> https://skydrive.live.com/redir?resid=2D1BE48F6B626811!146917

Yours sincerely,
Arvind.