Use backlinks (`` ) or nothing at all instead of single-quotes ('') around your field in the request:
$result = mysql_query("SELECT *, DATE_FORMAT(`timestamp`, '%W %D %M %Y') as date FROM articleDB WHERE userID='".$_SESSION["**"]."' ORDER BY timestamp DESC LIMIT 8");
Backticks (`` ) creates a reference to a table member, single-quotes creates a string ( '). You were basically trying to DATE_FORMAT the string "timestamp" .
, as , :
echo ' Posted: '.$row['date'];