UDF Range Argument Into Array Assignment

I having trouble with an intermediate step filling of an array based on the input range data and polynomial degree. The values calculated (xsum and xysum) for the array (F in the code) are accurate, but the function returns #VALUE for all elements.

Function poly_fit(ByVal Xdata As Range, Ydata As Range) As Variant
Dim a As Integer, b As Integer, c As Integer
Dim deg As Integer, num_pt As Integer
Dim Xs() As Variant, Ys As Variant
Dim F() As Variant, XY() As Variant, coef() As Variant
Dim xsum As Variant, xysum As Variant
Xs = WorksheetFunction.Transpose(Xdata)
Ys = WorksheetFunction.Transpose(Ydata)
If UBound(Xs) UBound(Ys) Then
MsgBox "You don't have the same number of X's and Y's"
End