error: mysql_fetch_array(): supplied argument is not a valid MySQL

$result = mysql_query("SELECT FROM at ORDER BY pubdate DESC LIMIT 25");

$AT_array;
$i=0;
while($row = mysql_fetch_array($result, MYSQL_NUM))
{
$AT_array[$i]=array($row[0],$row[1],$row[2],$row[3]);
$i++;
}

Why doesn't this work?. I'm tryig to store data from MySQL into an array.

$arr = array();

$result = mysql_query("SELECT FROM at ORDER BY pubdate DESC LIMIT 25");

while($row = mysql_fetch_array($result){ $arr += $row; }

The error you're getting means the query is invalid.
You're not actually telling mysql which fields you want to select, you should list them, separated by commas between 'SELECT' and 'FROM'
e.g.
SELECT id, name, birthday FROM at