Please find below my solutions to the 2 problems I encountered.

Problem 1 Solution: ProductAdmin.ascx.cs

protected void Page_Load(object sender, System.EventArgs e)
        {
            if (StoreSettings != null)
            {
                if (StoreSettings.CurrencySymbol != string.Empty)
                    LocalFormat.CurrencySymbol = StoreSettings.CurrencySymbol;

                _nav = new AdminNavigation(Request.QueryString);

                // Do we show list or edit view?
                if (_nav.ProductID != Null.NullInteger)
                    ShowEditControl();
                else
                    ShowProductList();
            }
        }

Problem 2 Solution: StoreAddress.ascx.cs

public void PopulateAddress()
        {
            if (addressInfo == null)
            {
                addressInfo = new AddressInfo();
                this.hiddenAddressId.Value = string.Empty;
            }

            if (addressInfo != null)
            {
                hiddenAddressId.Value = addressInfo.AddressID.ToString();
                chkUserSaved.Checked = addressInfo.UserSaved;
           .......
           .......
            }
}

Fresh install of DNN Store 3.0.0. I have already filled the Store Admin Settings. Go to "Account" module, select "Addresses". So I only have the registration address on the grid. I click "Add" then enter my information. When I hit "Update" the error is displayed.

The code I submitted for this bug is actually from the Store 2.1.36 version. I'm not sure why it was taken off.

Thank you for this great product.