I would use 1 instead of 001 but that shouldn't really make any difference, and for the summary type I would use "Sum" although again that shouldn't make much difference because it only affects report summary rows.
AA is fine in column names - we generally use lowercase as a convention to make it more obvious that it is a column rather than a stat name.
I can't see why your stat wouldn't work if you were able to save the column and the stat. We'd really need to see it to find out what was wrong so I'm afraid I have to ask you to attach it to a
Support Ticket - if you post the number here one of us will take a look at it for you.