Try this:
Public Function SeekExcel(XDate As Date, FolderPath As String) As String
Const SearchMask As String = "*siopsur*.xls*"
Const WrongMask As String = "*siopsurt*"
Const Months As String = "InSpain,Enero,Febrero,Marzo,Abril,Mayo,Junio,Julio,Agosto,Septiembre,Octubre,Noviembre,Diciembre"
Dim File As String, Folder As String
If Mid(FolderPath, Len(FolderPath)) = "\" Then Folder = FolderPath Else Folder = FolderPath & "\"
Folder = Folder & Year(XDate) & "\" & Split(Months, ",")(Month(XDate)) & "\" & Format(Day(XDate), "00") & "\"
File = Dir(Folder & SearchMask)
Do While (Len(File))
If Not LCase(File) Like WrongMask Then
SeekExcel = Folder & File
Exit Do
End If
File = Dir()
Loop
End Function