[resolved] What is wrong with this syntax?

[solitario]

$sql = mysql_query('SELECT golf_course_code FROM availability WHERE golf_course_code='.$_POST['txtGolfCourse'].' AND t_date="'.$temp_date.'"');
    while ($row = mysql_fetch_object($sql)) {\
        echo $row->golf_course_code.'<br>';
    } 

I'm getting this rather unhelpful error message:

Warning: mysql_fetch_object(): supplied argument is not a valid MySQL result resource in C:\golf_engine_php\xt_index.php on line 33

Any help is appreciated.
Many thanks.