Error creating tasks

I have the next method for creating tasks into a existing project:

public void CreateTask(string ProjectID, string TaskName
, string start, string duration)
{
try
{
Guid projectGuid = new Guid(ProjectID);
Guid sessionGuid = Guid.NewGuid();
const string SESSION_DESC = "description";

project.CheckOutProject(projectGuid, sessionGuid, SESSION_DESC);

dsProject = new
w2003wss1.ProjectDataSet(); w2003wss1.ProjectDataSet.TaskRow taskRow =
dsProject.Task.NewTaskRow();

Guid taskGuid =...

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