singular jacobian error by solvin 2.Order ODE with bvp4c and Parameters

hi there, i'm working for a while on this problem and hope someone could help me.

I want to to solve a BVP for a invertet double pendulum to get the parameters (p)for a swing-up trajectory.

unfortunately i get the error....

??? Error using ==> bvp4c at 252 Unable to solve the collocation equations -- a singular Jacobian encountered.

Error in ==> Trajectory at 11 sol=bvp4c(@ODE,@BC,solinit);

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clear all
close all

global T g

T=2.2;

g=9.81;

solinit = bvpinit(linspace(0,T,10),[1 1 0 0], [0 0 0 0]);
sol=bvp4c(@ODE,@BC,solinit);

----------------------------------------------------------

function dydx = ODE( x,y,p )

global  g T

l1=0.323;
l2=0.480;
a1=0.215;
a2=0.223;
m1=0.853;
m2=0.510;
J1=0.013;
J2=0.019;
d1=0.005;
d2=0.005;

n1=y(1);
np1=y(2);
n2=y(3);
np2=y(4);

G=[J1+a1^2*m1+l1^2      a2*l1*m2*cos(n1-n2)
   a2*l1*m2*cos(n1-n2)  J2+a2^2*m2        ];

a0=-p(1)-p(3);
a1=-p(2)-p(4);

Ypp= -(pi/T)^2*(a1*cos((1*pi*x)/T) ...
           +4*p(1)*cos((2*pi*x)/T) ...
           +9*p(2)*cos((3*pi*x)/T) ...
          +16*p(3)*cos((4*pi*x)/T) ...
          +25*p(4)*cos((5*pi*x)/T));

b=[d1*np1+d2*(np1-np2)+l1*m2*a2*sin(n1-n2)*np2^2-(a1*m1+l1*m2)*(g*sin(n1)+cos(n2)*Ypp)
   d2*(np2-np1)-a2*m2*(g*sin(n2)+l1*sin(n1-n2)*np1^2+cos(n2)*Ypp)];

n =G\b;

dydx=[y(2)
      n(1)
      y(4)
      n(2)];

end

------------------------------------------------------------------

function res = BC( ya,yb,p )

res=[ya(1)+pi
     ya(2)
     ya(3)+pi
     ya(4)
     yb(1)
     yb(2)
     yb(3)
     yb(4)];

end

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thanks a lot so far