"Select method of Range class failed" error

Here's the code. Any guesses as to why I get a run time error during execution?
thanks deb

Private Sub Worksheet_Change(ByVal Target As Excel.Range)
If Target.Interior.ColorIndex = vbCyan Then
MsgBox "Enter Seat Number in Box"
Else
Application.ScreenUpdating = False
Valx = Target.Value
Target.Value = "X"
Worksheets("Sheet2").Activate
ERROR Range("A1:A6").Select
Range("a1").Activate
If ActiveCell.Value = "" Then
ActiveCell.Value = Sheets("Sheet1").Range("G30").Value
ActiveCell.Offset(0, 1).Select
ActiveCell.Value = Valx
End If
End If
End Sub