Sage VAT Cash Accounting to Invoice Accounting

Has anyone changed from cash accounting for VAT to invoice accounting on sage.

I found some instructions which stated that all transactions must be reconciled.

So after doing the 30/6/10 return I reconciled all transactions, but when I came to do 30/9/10 return it still would not let me uncheck the cash accounting box, saying that all transactions must be reconciled. I then reconciled all transactions for 30/9/10 and it still wouldn't let me uncheck the box. I was doing 30/9/10 return in October.

Is it something to do with dates, should I ensure every transaction on the system right up to the current date is reconciled?

Thanks for any help.