can't insert a column

[Dorothy]

I'm new to the Mac OpenOffce spreadsheet. I read the directions for inserting a 
column, but instead of a column inserting, a get a message that says "filled 
cells cannot be shifted beyond the sheet". My entries so far only cover A to N 
and 1 to 100 so far, so this doesn't make sense to me. Why am I getting this 
message?