Need help with joins

I am having a nightmare with this query

SELECT Employee.ssn
FROM Employee
INNER JOIN Manages on Employee.ssn = Manages.ssn
WHERE
(SELECT COUNT(e.ssn) as SSN, d.dno
FROM Employee e
INNER JOIN Manages m ON e.ssn = m.ssn
INNER JOIN Works w ON m.dno = w.dno
INNER JOIN Department d ON w.dno = d.dno
GROUP BY e.ssn, d.dno
HAVING COUNT(e.ssn) > 5);

The bold bit is the original query where it finds all departments where these is more than 5 employees. I need to find the ssn of the employee who manages that department.

In MySQL it points to the nested select whereas in Oracle it says Too many values

Here is the table structure

I have been struggling to create this query all dat and am ready to give up

I want to select all employee_ids who manages a department with more than 5 employees

Employee table
-------------------
ssn (primary key)

Manages table
------------------
ssn(foreign key)
dno(foreign key)

Works_in table
------------------
ssn (foreign key)
dno(foreign key)

Department table
----------------------
dno(primary key)