buscar en otra hoja del mismo libro va pero de otro libro no. qu é

Function encuentra2(k As Range, kc As Integer, ka As Range, kb As Workbook)
Dim fi, co, ho As Integer
fi = ka.Row
co = ka.Column
book = Workbooks(kb)
ho = book.Worksheet.Index
While Worksheets(ho).Cells(fi, co).Value <> ""
If Worksheets(ho).Cells(fi, co).Value = k.Value Then
encuentra2 = Worksheets(ho).Cells(fi, co + kc).Value
Exit Function
Else
fi = fi + 1
End If
Wend
encuentra2 = Null
End Function

ESTO NO FUNCIONA

Function encuentra(k As Range, kc As Integer, ka As Range)
Dim fi, co, ho As Integer
fi = ka.Row
co = ka.Column
ho = ka.Worksheet.Index
While Worksheets(ho).Cells(fi, co).Value <> ""
If Worksheets(ho).Cells(fi, co).Value = k.Value Then
encuentra = Worksheets(ho).Cells(fi, co + kc).Value
Exit Function
Else
fi = fi + 1
End If
Wend
encuentra = Null
End Function

ESTE SI FUNCIONA