Fatal Error, on Bind Param. PHP Prepared Statements

Question

So I am stumped, I am getting:

Fatal error: Call to a member function bind_param() on a non-object in 'Website Address' on line 261

1. I have other queries of the exact same nature on other pages, and they work.
2. I have closed out all previous queries
3. I have checked spelling, punctuation of all tables/columns in the SQL database.
4. The $conn variable is the databse connection, and it works in other queries.

I feel like it is something simple, but I am just not seeing it.

Code:

$Key = $_GET["Key"];                                
$Select_Groups_Query = "
    SELECT Group_Name,
           Group_Key,
           Group_Members_User_Key, 
           Group_Members_Group_Key  
      FROM Group_Members 
     INNER JOIN Group ON Group_Members_Group_Key = Group_Key 
     WHERE Group_Members_User_Key = ?
";

$Select_Groups_stmt = $conn->prepare($Select_Groups_Query);

$Select_Groups_stmt->bind_param('s', $Key);                 
$Select_Groups_stmt->execute();             
$Select_Groups_stmt->bind_result($Group_Name, $Group_Key, $Group_Members_User_Key, $Group_Members_Group_Key);