Question: "solve" returns nothing.

Here is a sample code:

restart;
N := 3;

for i to 2 do

   f[i] := unapply(a[0][i]+Sum(a[j][i]*t^j, j = 1 .. N), t) end

do;

sys : = {diff(x(t),t) = y(t), diff(y(t),t) = x(t) }

syssub := subs([x(t) = f[1](t), y(t) = f[2](t)],sys)

simplify(syssub)

   solve(simplify(syssub) union {simplify(f[1](0))=2, simplify(f[2](0))=1}),
     {a[0][1], a[0][2], a[1][1], a[1][2], a[2][1], a[2][2]}
);

Now for some reason solve returns nothing. This doesn't make sense to me since the system is determinable.

Here is a proof,

 ans: = dsolve(sys union {x(0) = 2, y(0) = 1},{x(t), y(t)}, type = series)

will actually return the result.

The reason I am doing this is because I am currently working on a bigger nonlinear DE system and it couldn't be done with just dsolve and since there isn't a package in Maple that makes a series representation and plug and chug, I have to write out the necessary steps.

Something tells me that Maple has a lot of trouble getting around the variable "t". But it still makes no sense why it can't even return a[0][1] = 1,a[0][2]=2