Sage 50 automatically blocks transactions that are dated before  the start date of the previous  financial  year. If you see the option as grayed out and you are not allowed to select a date or getting Sage Invalid Date Error , please make sure you are in single user mode and all the other screens are closed. Now, follow the steps given below-

1. Click Setup,
2. Now go to Settings,
3. Navigate to Company and  System.
4. Click the option Do not allow transactions dated before <date>.
5. Enter the date of your choice in the field

You can also stop transaction prior to a specified date from being posted by using the Lock Date feature.  If anyone tries to post a transaction prior to this date, he will receive an error message.  However,  if you are logged in as manager or you have the lock date access, you can override the warning and post such transactions.

Here is how to set a Lock date–

• Go to the Menu bar
• Click on Settings
• Now click on Lock Date
• Select the check box named Lock posting before
• Enter the date of your choice
• Click OK

You can also configure the Lock Date access rights of any user, to prevent accidental posting-

1. Open Sage Accounts
2. Log in as Manager.
3. Go to the menu bar
4. Click Settings then on  Access Rights.
5. From the list, select the required user
6. Click the  Edit tab
7. Expand theSettings 
8. If you want to grant access to override the lock date, click the check box named  Lock date settings and click OK . To remove access, uncheck  the check box.
9. Click OK
10. Click Close to complete