After you've completed your month-end tasks, you should lock that period using the Lock Periods feature. This will prevent anyone from inadvertently making an entry in a period in which you don’t want new entries. To do this:
Go to the Setup menu and choose Preferences. The Preferences window appears.
Click the Security tab.
Select the Lock Periods: Disallow Entries Prior to option, and select the relevant date. This selection places a temporary lock on the date you select and the period before it. If you need to make an entry in a locked period at a later time—for example, you locked 31st of May, and now want to make an entry in April— you can unlock that date in the Preferences window.