Assigned To column is blank though set from VS 2010 workflow

Hi

I am trying to create a sequential approval workflow for a SharePoint list "Requests". End user can select theApprover (people/group field) while submitting a new request.

In the workflow code at "Create task" activity I am setting the task properties as shown below. 

Now the item is getting created in Task list but the "Assigned To" field is blank..am I missing anything..?

 private void createRequestTask_MethodInvoking(object sender, EventArgs e)
        {
            // Now create the approval task.
            SPListItem currentItem = workflowProperties.Item;



            // Set up some of the properties.
            RequestApproveTaskId = Guid.NewGuid();
            RequestTaskProperties.Title = workflowProperties.Item["Title"].ToString() + " is ready for review";
            RequestTaskProperties.Description = "Please review the request and approve or reject it.";
            RequestTaskProperties.AssignedTo = currentItem["Approver"].ToString();

            LogComment("Request Task Created.");

        }

Please suggest.