Brute-forcing with a recursive function a chess knight puzzle

I want to solve a chess knight puzzle (it is for the testament of sherlok holmes game )

I have a 8x8 size chess board and the knight starts at (0,0). I got to find a sequence of moves to cover every spot on the chess board. (I suppose everyone knows the actual knight allowed movement in chess)

Here is my code, but I can't find what is wrong with it. Looking at the output, after some moves it sometimes chooses the wrong square to move to ...

<?php

echo "\n  - Knight puzzle brute forcer by VGA - \n";
$currpos = array(0,0);
$occupiedpositions = array();
$validpositions = getvalidmoves($currpos, $occupiedpositions);

print_r ($validpositions);

function getvalidmoves($currpos, $occupiedpositions) {

	$validpositions = array(
		array($currpos[0]+1,$currpos[1]-2),
		array($currpos[0]+2,$currpos[1]-1),
		array($currpos[0]+2,$currpos[1]+1),
		array($currpos[0]+1,$currpos[1]+2),
		array($currpos[0]-1,$currpos[1]+2),
		array($currpos[0]-2,$currpos[1]+1),
		array($currpos[0]-1,$currpos[1]-2),
		array($currpos[0]-2,$currpos[1]-1)
	);
	
	foreach ($validpositions as $key => $pos) {
		if (($pos[0] < 0) || ($pos[0] > 7) || ($pos[1] < 0) || ($pos[1] > 7) || in_array($pos,$occupiedpositions)) {
			unset($validpositions[$key]);
		}
	}
	
	if (sizeof($validpositions) > 0) {
		if (sizeof($occupiedpositions) == 62) {
			echo "SUCCESS !!!!!!!\n";
			print_r ($occupiedpositions);
			exit;
		}
	} else {
		echo "FAILURE after ",sizeof($occupiedpositions)," moves \n";
		return;			
	}
	
	foreach ($validpositions as $key => $pos) {
		array_push($occupiedpositions,$currpos);
		$currpos = $pos;
		getvalidmoves($currpos, $occupiedpositions);
	}
	
	return;
}
?>