FD problem: "vector too small"

Hi,

I'm using the FD solver in GNU prolog to solve a couple of problems
over at http://ProjectEuler.net. The problem I'm currently solving is
this: http://projecteuler.net/index.php?section=problems&id=39:

If p is the perimeter of a right angle triangle with integral length
sides, {a,b,c}, there are exactly three solutions for p = 120.

{20,48,52}, {24,45,51}, {30,40,50}

For which value of p 1000, is the number of solutions maximised?

This sounds like an excellent problem for applying some CLP/FD, I
thought, and wrote this program:

perimeter([P,X,Y,Z]) :-
	X #>= 1,
	Y #>= X,
	Z #>= Y,
	P #= X + Y + Z,
	X ** 2 + Y ** 2 #= Z ** 2,
	fd_all_different([X,Y,Z]),
	fd_labeling([P,X,Y,Z]).

p39(0, Length, Length).
p39(P, MaxLen, Length) :-
	findall([X,Y,Z], perimeter([P,X,Y,Z]), Solutions),
	length(Solutions, NewLen),
	max_list([NewLen, MaxLen], NewMaxLen),
	P0 is P - 1,
	p39(P0, NewMaxLen, Length).

p39(MaxLen) :-
	p39(1000, 0, MaxLen).

but when I run it, I get lots and lots of warnings on the form:

    Warning: Vector too small - maybe lost solutions (FD Var:_54)

What does this warning mean? And how do I avoid getting it?

-- 
/Jesper