Hopefully there is a solution to my quandary this time. I am trying to
evaluate cells in a list to confirm that they are in a validation list.
Yes, I know that validation should have been used during entry, but it
was circumvented and I want to cycle through the cells and highlight
any that are not in the validation list.

My problem is that the following example code works when addressing a
range by cell reference (i.e. "c2:c9") and with a defined name range
that is limited (i.e. Shifts = "f3:f6"). But when I make the defined
name range dynamic, it stops working (i.e. Shifts =
offset(f3,0,0,counta(f3:f100),1) ). The cell loop goes across the
entire sheet, as it was from a more complicated example.

Could someone please explain what I am missing here?

Sub checkvalidation()
Dim LastRow As Long, LastCol As Long, rowstep As Long, colstep As Long,
validtype As Long
Dim validrng As Range

Application.EnableEvents = False
Application.ScreenUpdating = False

On Error GoTo errhandler

LastRow = Cells.SpecialCells(xlLastCell).Column
LastCol = Cells.SpecialCells(xlLastCell).Column

On Error Resume Next

For colstep = 1 To Last Col
For rowstep = 1 To LastRow
validtype = Cells(rowstep, colstep).Validation.Type
If validtype = 3 Then
Set validrng = Range("shifts")
If
IsError(Application.WorksheetFunction.Match(Cells( rowstep, colstep),
validrng, 0)) Then
With Cells(rowstep, colstep)
.Interior.ColorIndex = 45
End With
End If
End If
Next rowstep
Next colstep

errhandler:
Application.ScreenUpdating = True
Application.EnableEvents = True
Exit Sub

End Sub