Hello,
I believe there is some other module still open. That's why the Dynamics SL does allow you to close the GL.
Normally what we do before Closing the General Ledger, You have to close the Accounts Payable, Purchasing, Accounts Receivable, Inventory, Cash Manager, Bank Reconciliation & Pay roll(Optional) if you haven't have the license for the Pay Roll. You have to do the proper closing for each module.
NOTE: If there is any unreleased batch available in any module, The SL won't allow you to close.
Thanks,
Perumalsamy R.