PHP array_key_exists does not work; array is not multi-dimensional

I have an array of all the countries in the world as such:

$countries = array(
  "GB" => "United Kingdom",
  "US" => "United States",
  "AF" => "Afghanistan",
  "AL" => "Albania",
  "DZ" => "Algeria",
  "AS" => "American Samoa",
  "AD" => "Andorra",
  "AO" => "Angola",
  "AI" => "Anguilla",
  "AQ" => "Antarctica",
  "AG" => "Antigua And Barbuda",
  "AR" => "Argentina",
  "AM" => "Armenia",
  "AW" => "Aruba",
  "AU" => "Australia",
  "AT" => "Austria",
  "AZ" => "Azerbaijan",
  "BS" => "Bahamas",
  "BH" => "Bahrain",
  "BD" => "Bangladesh",
  "BB" => "Barbados",
  "BY" => "Belarus",
  "BE" => "Belgium",
  "BZ" => "Belize",
  "BJ" => "Benin",
  "BM" => "Bermuda",
  "BT" => "Bhutan",
  "BO" => "Bolivia",
  "BA" => "Bosnia And Herzegowina",
  "BW" => "Botswana",
  "BV" => "Bouvet Island",);

And so on for all countries; I am 100% positive every country is listed properly.

I have an application form which stores the result in a file stored on the server. Currently the review page for the application is a basic text version and I am now in the process of putting it into a mock-form for my client to have a more visually appealing method of reviewing applications.

So an array named $in_data stores the results that come from the file. This array is structured as such "emergency_medical_insurance" => "value_user_entered". Each key is the name of the HTML element it came form and the value is what the user put in.

The country select list on the form returns a two-letter code of the country. So what I am trying to do is search $countries with the value of $in_data['country_select'] and then return the name of the country.

echo $in_data['country_select']; returns 'CA' the letter code for Canada and the test country I have entered.

echo $countries['CA']; returns 'Canada'

if (array_key_exists($in_data['country_select'], $countries)){ 
      echo "Country Found";
} 
else { echo "failed"; }

returns nothing.

if (array_key_exists('CA', $countries)){ 
      echo "Country Found";
} 
else { echo "failed"; }

Also returns nothing. And when I say nothing I mean nothing, not null, not true, not false; just doesn't even run.

My question is simple; how is the code below (taken from the offical PHP manual) which does EXACTLY the same thing my code does, working, but my code won't even return anything?

<?php
$search_array = array('first' => 1, 'second' => 4);
if (array_key_exists('first', $search_array)) {
    echo "The 'first' element is in the array";
}
?>

since you are reading from a file, you may be getting other characters, try trim():

if (array_key_exists(trim($in_data['country_select']), $countries)){ 
      echo "Country Found";
} 
else { echo "failed"; }