Inputbox Method NOT Returning Multi-cell Range Object

I have the following code in Destination.xlsm that is intended to:

request the user to select a multi-cell range in a column of single-sheet Source.xlsm, in which some but not all cells contain "Y" (to indicate that this row of data relates to a National Account, versus a Territory Account)loop through the selected range, and whenever a cell contains "Y", copy the entire row and insert it in Destination.xlsm above a cell named "rngDest".

Code:

Sub Copy_NationalAccounts_Rows()

Const Message As String = "Select the entire range containing National Account Y flags, then press Enter or click OK."
Const Title As String = "Copy National Accounts"

Dim rngSource As Range
Dim rngDest As Range
Dim r As Range
Dim c As Integer
Dim wbk As Workbook

[Code] ........