This is the field that groups the actual dates together:
DEPOSIT DATE By Month: Format$([Deposit Query].[DEPOSIT DATE],'mmmm yyyy')
Then, there's the field you suggested to sort the month by number:
MonthNumber: Choose([DEPOSIT
DATE],"Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec")
My first thought is that maybe the choose function should be full months and years, ie. "January 2011"?
Also, what happens when you have Jan 2011 & Jan 2012 for example if you just use "Jan"?
Thanks.