Make Udf Function Get Range From Otherworkbook

i need to create a udf that will take a cell parameter and then emulates( i guess thats the best word) the index/match functions. the reason im doing this - and not the index/match - is because excel has ran out of memory on me (external links stuff).

Set XLBookInventaire = Application.Workbooks.Open(strFilePathInventaire & "" & strFileNameInventaire, False, True)
line, the XLBookInventaire is still nothing

i believe its a limitation of the excel udfs, but i dunno how to avoid it or how to make this function work.

Function RechercherProduit1(cell As range)
Dim XLBookInventaire As Workbook
Dim MyCurrentSheet As Worksheet
Dim bNotOpenInventaire As Boolean
Dim XLSheetInventaire As Worksheet
Dim rngInventaire As range
Dim strFileNameInventaire As String
Dim strFilePathInventaire As String
Dim FaceArrInventaire() As Variant
Dim FaceRowInventaire As Long
Dim LastRowBColumn As Long, LastRowInventaire As Long
Dim LastWindowState As XlWindowState

LastWindowState = ActiveWindow.WindowState
Set MyCurrentSheet = Application.ActiveSheet
Application.ScreenUpdating = False.......................................