Msgbox all empty rows in a range

I see now. The end(xlup) skips past the hidden rows at the bottom of your used range. So we need to find the last used cell in column B a slightly different way:

Sub Blankcells3()
    Dim r As Range, l As Long
    On Error GoTo NoBlanks
    l = 191
    Do Until Cells(l, 1).Value <> ""
        l = l - 1
    Loop
    Set r = Range("C18:C" & l).SpecialCells(xlCellTypeBlanks)
    MsgBox "Blank cells in " & Replace(r.Address(False, False), "C", ""), vbInformation + vbOKOnly, "Blanks"
    Exit Sub
NoBlanks:
    MsgBox "No blank cells found", vbInformation + vbOKOnly, "Blanks"
End Sub

Better?