Excel 2007 : Why am I getting this 1004 error?

Hello folks,

Below is a block of code that is attempting to first find the last Row number of some imported data on a spreadsheet (A), then take a value entered by the user (on a different sheet B) and paste it into another column of the original spreadsheet (A). only pasting the same number of rows as was determined to be in the imported data.

The determination of the last Row number (LastRow) seems to work fine.

The pasting part of the code works just fine if I hard coded a value for the last Row number (like use 6725 instead of "LastRow").

But when I try to use my "LastRow" variable in the pasting code, I get an error:

"Run-time error '1004':
Application-defined or object-defined error"

And clicking the Debug button highlights the line (in yellow):

.Range(.Range("L4"), .Range("L" & "LastRow")).Value = Target.Value

Any idea why I am getting this error here?

Sub Worksheet_Change(ByVal Target As Range)

    With Sheets("AIO-Cond").Range("A1")
        With .Cells(.Rows.Count, Range("A1").Column)
            If Not IsEmpty(.Value) Then
                LastRow = .Row
            ElseIf IsEmpty(.End(xlUp)) Then
                LastRow = ""
            Else
                LastRow = .End(xlUp).Row
            End If
         End With
    End With
    
    If Target.Address = "$D$4" Then
    With Sheets("AIO-Cond")
    .Range(.Range("L4"), .Range("L" & "LastRow")).Value = Target.Value
    End With
    End If

    If Target.Address = "$D$5" Then
    With Sheets("AIO-Cond")
    .Range(.Range("M4"), .Range("M" & "LastRow")).Value = Target.Value
    End With
    End If

    If Target.Address = "$D$6" Then
    With Sheets("AIO-Cond")
    .Range(.Range("N4"), .Range("N" & "LastRow")).Value = Target.Value
    End With
    End If

End Sub