1) You have a unit mismatch. m.i*g is force (N, or kg*m/s^2) but k.i is kg/(m^2*s^2) and x.i are dimensionless.
So either let the vector x be m^3 or set the unit for k.i to N.
2) The last line in your solve block is nonsense. How can a row vector (1x5 matrix) equal a scalar (sum of the five vector elements of x)? Furthermore you already have five equation for your five variables.