Wrong answer with a derivative on a desolve

[MrBonheur]

Hi,

I have a problem with a difficult operation. I need to solve :
d/dx(E*S0*(1-x/l)*du/dx) = rho*g*s0*(1-x/l) with u(0)=0.
So I try on my TI :
desolve( d(E*S0*(1-x/l)*u',x) = rho*g*S0*(1-x/l) and u(0)=0, x, u).

The calc answer me :
u=g*rho*x*(x-2*l)/(2*E)
but the correct answer is :
u=g*rho*x*(x-2*l)/(4*E).

Is anyone know what may be the problem is ?

Thanks.