How to create task in Sequential Workflow?

Hi,

I created Sequential Workflow for SP2013 Custom List. Cod is below.

public sealed partial class SequentialWF : SequentialWorkflowActivity
    {
        public SequentialWF()
        {
            InitializeComponent();
        }

        public Guid workflowId = default(System.Guid);
        public SPWorkflowActivationProperties workflowProperties = new SPWorkflowActivationProperties();
        public Guid createTask1_TaskId1 = default(System.Guid);
        public SPWorkflowTaskProperties createTask1_TaskProperties1 = new Microsoft.SharePoint.Workflow.SPWorkflowTaskProperties();

        private void createTask1_MethodInvoking(object sender, EventArgs e)
        {
            createTask1_TaskId1 = Guid.NewGuid();

            createTask1_TaskProperties1.Title = "Task";

            createTask1_TaskProperties1.Description = "Please appraise the form";

            createTask1_TaskProperties1.StartDate = DateTime.Now;

            createTask1_TaskProperties1.AssignedTo = "...@....com";
        }
    }

When I created list item then error occurred in the workflow.

What might be the reasons for the error?