Is "Z" and "z" two different variables? What are you solving for? I'll assume they're the same variable and that you're wanting to solve for z.
z^2 – 5*(1 + i)*z + 2 + 14*i = 0
There is no such z that will satisfy that equation.
AfterShock's factoring method is better than this one, but remember any quadratic with real or complex coefficients may be solved using the quadratic formula. The solution in this case is a bit of a mess (which is why I recommend factoring whenever possible) but will work.