If you filter Null in the first query:
SELECT TableTaskAssign.TaskAssignID, TblTask.TaskDesc, TablePerson.Name, TblTask.TaskValue, TableTaskAssign.CompDate
FROM TblTask RIGHT JOIN (TablePerson RIGHT JOIN TableTaskAssign ON TablePerson.PersonID = TableTaskAssign.PersonID) ON TblTask.taskID = TableTaskAssign.TaskID
WHERE (((TableTaskAssign.CompDate) Is Null));
And don't use the CompDate field in the 2nd query because you already know that all the records are not completed.
SELECT QryTask01.Name, QryTask01.TaskDesc, Sum(QryTask01.TaskValue) AS SumOfTaskValue, Count(QryTask01.TaskDesc) AS CountOfTaskDesc
FROM QryTask01
GROUP BY QryTask01.Name, QryTask01.TaskDesc;