Warning: Cannot find explicit solution. > In solve (line 318)

I am having trouble solving a system of two equations with two variables. Previously I have solved less difficult systems of equations this way. What could I be doing wrong? I am using version R2015a. Value a is a parameter.

Program code:

syms x alpha a

Z = ((x^2)/8)*(sqrt(1-sin(alpha)^3))*(12*(a^4)-(5*a*x)*(7-sin(alpha))+((4*(x^2))*(5-3*sin(alpha)+4*sin(alpha)^2)));

Zx = diff(Z,x) == 0;

Zalpha = diff(Z,alpha) == 0;

eqns = [Zx, Zalpha]

sol = solve(eqns, x, alpha);

Xsol = simplify(sol.x,'steps',20);

ALPHAsol = simplify(sol.alpha,'steps',20);

Xsol

ALPHAsol

Result:

Warning: Cannot find explicit solution.

> In solve (line 318)

Xsol =

Empty sym: 0-by-1

ALPHAsol =

Empty sym: 0-by-1