Warning: mysql_fetch_array() expects parameter 1 to be resource, boolean given in - p

Warning: mysql_fetch_array() expects parameter 1 to be resource, boolean
given in - p

Im getting an error: Warning: mysql_fetch_array() expects parameter 1 to
be resource, boolean given in
I tryed everything I cant seem to figure out where the problem is, would
somebody help
if ($number == 1) {
$row = mysql_fetch_array($r);
if ($return == "array") $res = $row;
else if ($return == "object") {
if ($obj == "Gallery") $res = new $obj($row["id"]);
else {
$obj = str_replace("_", "", $obj);
$res = new $obj($row);
}
}
} else {
$res = Array();
while ($row = mysql_fetch_array($r)) {
if ($return == "array") $res[] = $row;
else if ($return == "object") {
if ($obj == "Gallery") $res[] = new $obj($row["id"]);
else {
$obj = str_replace("_", "", str_replace("MM_", "",
$obj));
$res[] = new $obj($row);
}
}
}
}
return $res;