First, try putting brackets in around the scope of your first "using" statement. You can also do the same with the TaskService instance. You could do this by doing:
List<TaskInfo> taskList = new List<TaskInfo>();
using (TaskService ts = new TaskService(REMOTE", "username", "domain", "password", osVer.Contains("2003")))
{
EnumFolderTasks(ts.RootFolder, taskList);
}
DataContext = taskList;