Copying Between Sheets Using VBA

I'm strugling to write some VBA code, it's a bit untidy at present but it works untill I try to import values from sheet 2 to sheet1, I get an object error, but it dosen't mean anything to me.

Basically this code looks at sheet2 if the data is the same it overwrites it with upto date data, else it will add new unique enteries
to the last row.

Sub Importer()
Dim y As Integer
Dim z As Integer
Dim R As Long
'database
Sheets("Sheet1").Select
Cells(1, 1).Select
Range(Selection, Selection.End(xlDown)).Select
R = Selection.Rows.Count
'daily data
Sheets("Sheet2").Select
Cells(1, 1).Select
Dim Amax As Integer..........................