To learn why a non-zero amount remains to be allocated

Accounts > Maintaining accounts > Creating accounts > Opening balances -- Overview > To enter detail accounts' opening balances >>

Your list of accounts is out of balance if a non-zero amount appears in the "Amount left to be allocated" field at the bottom of the Enter your opening balances window. There are several reasons why your accounts may be out of balance:

Note:  What is the Historical Balancing account?