Vlookup Code For Non Active Sheet

I wrote this code today and it works - sometimes. Really it only seems to work when I have one of the sheets(zvur013) is in focus (ie, it was the last sheet to have been tabbed to). I dont understand what I'm missing, please help.



Sub lookforitems()
Dim items()
Dim groupnums()
Application. ScreenUpdating = False

Set allitems = Workbooks("zvur013.dbf").Sheets("zvur013")
Set allgnums = Workbooks("Groupnumbers.xls").Sheets("sheet1")
Countgroups = Application.WorksheetFunction. CountA(allgnums.Columns(1))
countitems = Application.WorksheetFunction.CountA(allgnums.Rows(1))
...........................
allgnums.Cells(j + 1, i + 2).Value = x
Debug.Print x
Next j
Next i

End Sub