decrementing counter causes error [ve][53]

<script type="text/javascript">							
	<!-- hide from incomparible browsers
		
		if (direction == "right") {			// if statement to determine  we 
increment the pointer
			++curHorse;			// if moving to right then increment counter curHorse
		}
		else if (direction == "left") {		// if statement to determine  we 
decrement the pointer	
			--curHorse;			// if moving to right then decrement counter curHorse	
		}
	// stop hiding from incompatible browsers -->
</script>

creates an error      should it ?

regards
Garth