Not sure what that param dfText is but the following worked fine:
Code:
Dim myDateDiff As Long
Dim myDate1 As New Date(2001, 12, 25)
Dim myDate2 As New Date(2002, 12, 25)
myDateDiff = DateDiff(DateInterval.Day, myDate1, myDate2)
MessageBox.Show(myDateDiff.ToString)