excel macro for loop code error

Hi everyone,

I have a for loop macro to go through a list of sheet names but it keeps quitting out. i'm hoping someone can help me and let me know what is wrong with my code

My for loop is going through each sheet and the sheetlist is in Summary starting at A15. it seems to work for the first sheet in the list but then on the second sheet it gives me a subscript out of range error

code below

dim  i as long

For i = 16 To Sheets("Summary").Cells(Rows.Count, 1).End(xlUp).Row + 1
    With Sheets(i - 1)
         sname = Worksheets("Summary").Range("A" & i - 1).Value
         Sheets(sname).Select
         Range("M20:M" & lastrow).Select
         Selection.Copy

    End With
Next i

can someone tell me where i went wrong with the code

thanks for everyone help.