How to solve 'Subscripted assignment dimension mismatch.' error?

s=285; l=360; w=2*481.37; d=36.9; alpha=(284.2/180)*pi; y=137;

syms fi

for i=1:451
    x=Px(i);
    eq = ((((-w/2)+d*sin(alpha-fi))-((-l/2)-x))^2)+(((d*cos(alpha-fi))-(-y))^2) == s^2;

      Fi(i)=vpasolve(eq,fi);

end

also Px variable is known.

Error:

Error using subsasgn Subscripted assignment dimension mismatch.

Error in sym/privsubsasgn (line 997) L_tilde2 = builtin('subsasgn',L_tilde,struct('type','()','subs',{varargin}),R_tilde);

Error in sym/subsasgn (line 834) C = privsubsasgn(L,R,inds{:});

Error in general_solve_1 (line 41) Fi(i)=vpasolve(eq,fi);