I am trying to solve a system of equations with Maple 16, but it keeps returning an error message. I have the following very simple code:

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assume(lambda > 0);

assume(kappa > 0);

assume(omega > 0);

assume(a >= 0);

assume(alpha, 'real');

assume(b >= 0);

assume(beta, 'real');

assume(m >= 0);

assume(mu, 'real');

assume(n >= 0);

assume(nu, 'real');

assume(t >= 0);

assume(tau, 'real');

assume(p >= 0);

assume(psi, 'real');

assume(d >= 0);

assume(delta, 'real');

assume(r >= 0);

assume(rho, 'real');

assume(x >= 0);

assume(xi, 'real');

solve({d^2*lambda^2+r^2*kappa^2+(x^2-1)*omega^2 = 0, (a^2-1)*lambda^2+m^2*kappa^2+t^2*omega^2 = 0, a*exp(-I*alpha)*b*exp(I*beta)*lambda^2+m*exp(-I*mu)*n*exp(I*nu)*kappa^2+t*exp(-I*tau)*p*exp(I*psi)*omega^2 = 0, a*exp(-I*alpha)*d*exp(I*delta)*lambda^2+m*exp(-I*mu)*r*exp(I*rho)*kappa^2+t*exp(-I*tau)*x*exp(I*xi)*omega^2 = 0, b*exp(-I*beta)*d*exp(I*delta)*lambda^2+n*exp(-I*nu)*r*exp(I*rho)*kappa^2+p*exp(-I*psi)*x*exp(I*xi)*omega^2 = 0}, {a, b, d, m, mu, n, nu, p, psi, r, rho, t, tau, x, xi, alpha, beta, delta}, useassumptions, maxsols = 10)

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When this piece of code is executed, I receive the following error message:

*Error, (in Engine:-Tarjan) invalid input: subs received {0 <= x_8, 0 <= x_10, 0 <= x_12}, which is not valid for its 1st argument*

What does this mean? How can I find solutions to this system of equations? (I *know* that there exists at least one solution, and I am figuring out whether there exist more.)

Any help would be greatly appreciated.