I keep getting this error message with my spreadsheet and I do not
know what it means. Can anyone help.

Error Message :
The sort reference is not valid. Make sure that it's within the data
you want to sort, and the first SORT BY box isn't the same or blank


Below is my source code:
For Each w In Worksheets
w.Activate
ActiveCell.SpecialCells(xlLastCell).Select
lnRange = CInt(Mid(ActiveCell.Address(RowAbsolute:=False), 3, 5))
lcCellRange = "A3:G" & Trim(Str(lnRange - 1))
w.Range(lcCellRange).Select
Selection.Sort Key1:=Range("C3"), Order1:=xlAscending,
Header:=xlNo, _
OrderCustom:=1, MatchCase:=False, Orientation:=xlTopToBottom

w.Range("A1").Select
Next w