If you a re using QuickBooks Online you can navigate to the Company Cog in the top right hand side of the screen and select account and settings. Under the advanced tab there is an option that says 'Close the books'. You will most likely find that this is ticked. Untick it and it will allow you to reconcile without this messasge coming up. However if you do make changes to transactions through the reconciliation screen this will change data in the system histroically. Unfortunately there is no way of avoiding this.