Excel VBA - Overflow error on Range select

Question

I am having an error when I try to select cells from a sheet:

  Dim ABHdataPath As String
  Dim ABHdataFile As Excel.Workbook

  ABHdataFile.Sheets("Booked").Activate ' make sure program starts from correct sheet
        ColumnName = ColumnLetter(ABHdataFile.Sheets("Booked").Cells(5, Columns.Count).End(xlToLeft).Column)
        ABHbooked = ABHdataFile.Sheets("Booked").Range("B5:" & ColumnName & Cells(Rows.Count, "B").End(xlUp).row).Value

When running above line, I get this error:

It doesn't give me any option to debug the code, so I find it hard to locate the error.

EDIT I have been able to debug my code, this is where it ends:

ABHBooked = ABHdataFile.Sheets("Booked").Range("B5:" & ColumnName & Cells(Rows.Count, "B").End(xlUp).row).Value

Debug:

ABHBooked = Empty

Rows.Count = 1048576

xlUp = -4162

ColumnName = CD

Answer 1

The function gives error whenever the ColumnNumber is less than 1. Thus, introduce a small check and it should work:

Function ColumnLetter(ColumnNumber As Long) As String
    Dim n As Long
    Dim c As Byte
    Dim s As String

    If ColumnNumber < 1 Then
        ColumnLetter = "NAN"
        Exit Function
    End If

    n = ColumnNumber
    Do
        c = ((n - 1) Mod 26)
        s = Chr(c + 65) & s
        n = (n - c) \ 26
    Loop While n > 0
    ColumnLetter = s

End Function

Answer 2

The problem was not that my variable wasn't stored as long , but rather the format of my selection.

This fixed the issue:

Selection.NumberFormat = "General”