String Names In Different Subs

How can it be that this works?

Sub AA()
Dim ReportFileName As String
Cells(1, 19).Select
ReportFileName = ActiveCell.Value
ChDir "C:"
Workbooks.Open Filename:=ReportFileName _
End Sub

And this doesn't work?

Sub BB()
Dim ReportFileName As String
Cells(1, 19).Select
ReportFileName = ActiveCell.Value
CC
End Sub
Sub CC()
ChDir "C:"
Workbooks.Open Filename:=ReportFileName _
End Sub

Somehow it seems that the value of the string "ReportFileName" is forgotten when running the subroutine CC. How do I make it not "forget" the file name?