Error - Object variable not set (Error 91)

Hi everybody Nice to meet you. I need some help with VBA.

I have worksheet, like this:

http://radikal.ru/F/s15.radikal.ru/i...03dc3.jpg.html

I have day-list. When i choose a day from this list, Excel should take me to another cell. This cell is ilustrated on third picture - column AK.

http://radikal.ru/F/s59.radikal.ru/i...e331f.jpg.html

http://radikal.ru/F/i061.radikal.ru/...3a719.jpg.html

But when I choose day on list I have this error:

Object variable not set (Error 91)

When I click Debug button Escel shows me, that this line is wrong in VBA:

Columns("AK").Find(what:=Target.Value, Lookat:=xlWhole).Select

This is my all code for this function:

Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Count = 1 Then
If Target = Range("C1") Then
  Columns("AK").Find(what:=Target.Value, Lookat:=xlWhole).Select
End If
End If

End Sub

What I do wrong ??

P.S. My sheets have to be protect in Excel.

Thanks for any help.