Declaring errors

Look at VB Help under Cell Error Values, where the following appears:

This example displays a message if the active cell on Sheet1 contains a cell error value. You can use this example as a framework for a cell-error-value error handler.

Worksheets("Sheet1").Activate
If IsError(ActiveCell.Value) Then
    errval = ActiveCell.Value
    Select Case errval
        Case CVErr(xlErrDiv0)
            MsgBox "#DIV/0! error"
        Case CVErr(xlErrNA)
            MsgBox "#N/A error"
        Case CVErr(xlErrName)
            MsgBox "#NAME? error"
        Case CVErr(xlErrNull)
            MsgBox "#NULL! error"
        Case CVErr(xlErrNum)
            MsgBox "#NUM! error"
        Case CVErr(xlErrRef)
            MsgBox "#REF! error"
        Case CVErr(xlErrValue)
            MsgBox "#VALUE! error"
        Case Else
            MsgBox "This should never happen!!"
    End Select
End If