How to prevent transactions in the previous fiscal year or any specific date?

Preventing transactions.

In the main page of Sage 50, go to Setup, Settings, Company, System.
Put a checkmark in Do not allow transactions dated before.
Enter the end date of the previous fiscal year, or any date for which you do not want transactions to be posted or modified.
Click OK to confirm the change.
Only transactions posted after the date put in Step 3 are now possible.