If you are using jonmo1's method, make sure you have not changed anything to the worksheet (or save) and there isn't any date cell formatting as it picks it up.
Sub PlugBlanks()
Dim ws As Worksheet
Set ws = ActiveSheet
ws.Range("B:B").SpecialCells(xlCellTypeBlanks).Value = 1
End Sub
So does your macro
UsedRange.Rows.Count is also subject to whatever Excel thinks is the last used row.
To prevent that, you would need to use an adjescent column to determine the last row to apply this to..Say column A for example
And change this line
LR = ActiveSheet.UsedRange.Rows.Count
to
LR = ActiveSheet.Cells(Rows.Count, "A").End(xlup).Row