Hello shrimic ,

The problem is with how you are using the Find method. Find returns a Range object if the search was successful. If not then it returns the special object Nothing. You should always check the result of the Find before you attempt to get the address, row or column.

Try this corrected version of your macro...
Option Explicit


Sub DRSummary()

Dim PartRngWorkbook1DRAMSheeta As Range, PartRngWorkbook1DRAMSheetb As Range
Dim cs As Variant, Cell1 As Long, Cell2 As Long, rngMultiply As Range, Cell4 As Long, Cell5 As Long
Dim Cell6 As Long, PartRngWorkbook1Reference1 As Range, a As Variant, wsActive As Worksheet, intCols As Integer, rngValue As Range
Dim Found As Range

Const intMultiplier As Integer = 10080
Dim ab As Worksheet, lastRow As Long

Set PartRngWorkbook1DRAMSheeta = Worksheets("DRAM").Range("A3", Worksheets("DRAM").Range("A65536").End(xlUp))
Set PartRngWorkbook1DRAMSheetb = Worksheets("DRAM").Range("B", Worksheets("DRAM").Range("B65536").End(xlUp))
Set PartRngWorkbook1Reference1 = Worksheets("Refer").Range("A", Worksheets("Refer").Range("A65536").End(xlUp))
Set ab = Worksheets("DRAM")

For Each cs In PartRngWorkbook1DRAMSheeta
    
    If IsNumeric(Application.Match(cs.Value, PartRngWorkbook1Reference1, 0)) Then
        Found = PartRngWorkbook1DRAMSheeta.Find(cs.Value)
            If Found Is Nothing Then GoTo NextCell Else Cell1 = Found.Row
       
        Found = PartRngWorkbook1DRAMSheetb.Find("WS Group Totals:", Range("B", Cell1))
            If Found Is Nothing Then GoTo NextCell Else Cell2 = Found.Row
        
      
       With ab
            intCols = .Cells(Cell2, .Columns.Count).End(xlToLeft).Column
            lastRow = .Rows(.Rows.Count).Row
                Set rngMultiply = .Range(.Cells(Cell2, 4), .Cells(Cell2, intCols))
                For Each rngValue In rngMultiply
                    .Cells(.Rows.Count, rngValue.Column).End(xlUp).Offset(2, 0).Value = intMultiplier * rngValue.Value
                Next
        End With
    End If
NextCell:
Next cs
End Sub