Bank Balance does not Agree with Balance Sheet

Bank Balance does not Agree with Balance Sheet

I have a issue in that the current balance in one of my bank accounts, does not agree with the balance sheet. 

My base currency is AUD

The bank account is a USD account and shows $35.56 which is correct. 
The balance sheet however shows the balance for this account as $531.94.  I realise that the balance sheet shows balances in AUD, but accounting for exchange the balance should be around $50 or thereabouts. 

Can someone please assist me with what may be the issue.

Thanks 
Jac