VBA: Problem importing date type to another file

[mafrej]

Hi, I've been trying to do a sumif with data from another excel file, I want to sum data from the other fille with a criteria based on dates from this same other file here's what i've done, but i get a error 13 type mismatch:

Private Sub Workbook_Open()

Dim XL As Excel.Application
Dim WBK As Excel.Workbook

'Date for comparision criteria
Set DateAc = Sheets("06-17").Range("E8")


Set XL = CreateObject("Excel.Application")
Set WBK = XL.Workbooks.Open(ThisWorkbook.Path & "\Budget-2013-14.xlsx")
Set Sh = WBK.Sheets("Transactions !")

'Date range and sum range form the other file
Set DateF = Sh.Range("B129:B134")
Set ValeurF = Sh.Range("F129:F134")



sauce = Application.WorksheetFunction.SumIf(DateF, "<" & DateAc, ValeurF) -The probleme is there

WBK.Close False


Set XL = Nothing
End Sub


I tried with a date and sum range from the file i'm working on without problem
I tried to only sum ValeurF without problem
I debbug to check the values contained in DateF and i seemed ok, but it is clearly my dates from the other file that cause the problem... any idea?

EDIT: I did a if and a for instead, saved me a lot of trouble, but i'm still interrested in the reason of the error knowing that if I replace the range of date from the other file for a range in the file i'm using, it is working perfectly