Bookkeeper will not allow any transactions prior to 1 year before the date you specify as the next year end.
For example, if you specify your next year end as December 31, 2003, you will not be able to enter transactions before January 1, 2003.
If you need to enter historical information, start with the earliest year end date that is after the first set of transactions you wish to enter. As you close the company's books, you will be able to set the next year end date.
If you have set the year end date to a wrong date you could either create a new company or perform a clean installation of the program. To create a new company, simply click Company and then select New Company. Directions on how to perform a clean installation of the program can be found in this article:
How can I completely remove and reinstall Bookkeeper? (KB010064)