I have a spreadsheet on the network for other users and someone changed the columns from A,B,C... to 1,2,3... This results in column A1 being identified as R1C1. A standard formula: =SUM(C5:C54) is now =SUM(R[-50]C:R[-1]C). My questions are how did someone make this change and how can I protect the spreadsheet from anyone making changes like this? Any help would be greatly appreciated.