The Cash Manager>Bank Rec>GL balance comes from the curyacct table. Verify the period in the Bank Rec record. If that is correct and this is a single currency database, do this.
Go into Initialization mode. Go into GL>Acct History. Change the beginning balance (at the bottom left of the screen) by a penny. Save. Change it back and save again. This updates the curyacct table. Now compare to Cash Manager>Bank Rec>GL balance.