连接到SQL Server数据库

.NET应用程序，通过该应用程序进行连接并按以下方式执行查询（包装在try-catch块中）：

using (SqlConnection conn = new SqlConnection(Configuration.connectionString))
{
    SqlCommand cmd = new SqlCommand(createTransactionQuery,conn);
    conn.Open();
    return cmd.ExecuteNonQuery();
}

查询字符串为：

createTransactionQuery = "BEGIN " +
                         "BEGIN Transaction" +
                         "  BEGIN TRY " +
                         "      --variables" +
                         "      DECLARE @varStaffID int;" +
                         "      DECLARE @varProductID int;" +
                         "      SET @varStaffID = " + transaction.getStaff().getID() + ";" +
                         "      SET @varProductID = " + transaction.getProduct().getProductID() + ";" +
                         " " +
                         "      --New record in Transactions table " +
                         "      INSERT INTO Transactions (Timestamp_, CustomerID, StaffID, ProductID) " +
                         "      VALUES (SYSDATETIME(),NULL,@varStaffID,@varProductID; " +
                         " " +
                         "      --Update inventory (Products table)" +
                         "      --First retrieve the current quantity of this product" +
                         "      DECLARE @varCurrQuantity int; " +
                         "      SET @varCurrQuantity = (SELECT Quantity FROM Products WHERE ProductID=@varProductID); " +
                         "      --and update it" +
                         "      UPDATE Products " +
                         "      SET Quantity = @varQuantity-1 " +
                         "      WHERE ProductID = @varProductID; " +
                         "  END TRY " +
                         "  BEGIN CATCH " +
                         "      ROLLBACK Transaction " +
                         "  END CATCH " +
                         "COMMIT Transaction" +
                         "END";

此代码引发异常：

System.Exception：'BEGIN'附近的语法不正确。

我知道可以更好的方式创建查询字符串。但是，我想知道问题的原因是什么，因为当在SQL Server Management Studio本身中执行此确切查询时，它就会起作用。

我已确保连接字符串正确，因为它在应用程序的其他部分完全可以正常工作。