Why have you changed it from "A:A" to "A:K" this part is only ever looking for the criteria number in the locate sheet, can this not always be kept in column "A" in the locate sheet? That way it will only count one column rather than "A:K" in the locate sheet.
[VBA]
Sub Highlighter()
Dim MyRange As Range, rCell As Range
Dim ShtStop As Integer
For Each pCell In ActiveWorkbook.Sheets
If pCell.Name = "Locate" Then Goto jump01
ShtStop = WorksheetFunction.CountA(pCell.Range("C:C"))
Set MyRange = pCell.Range("C1:C" & ShtStop)
For Each rCell In MyRange.Cells
If WorksheetFunction.CountIf(Sheets("Locate").Range("A:A"), rCell) > 0 Then
rCell.EntireRow.Font.ColorIndex = 3
rCell.Offset(, -1).Value = "Found"
End If
Next rCell
jump01:
Next pCell
End Sub
[/VBA]