problem saving test data to a file and then reloading it

I am having problems saving data from my HolidayPlannerTester program to file and then reloading it. The program compiles fine but when running the exception message is shown 'save failed'.

Here is my code please post if other code is required.

import java.io.*;

class ObjectFileUtility {

/* Writes an object to the named file. */
public static void saveObject(Serializable obj, String filename) throws IOException

{
ObjectOutputStream oos =
new ObjectOutputStream( new FileOutputStream(filename) );

oos.writeObject(obj);
oos.flush();
oos.close();
}
public static Object loadObject(String filename) throws IOException
{
ObjectInputStream ois =
new ObjectInputStream(
new FileInputStream(filename)
);

try
{
Object obj = ois.readObject();
ois.close();
return obj;
}
catch (ClassNotFoundException e) {
throw new IOException("ClassNotFoundException");
}
}
}

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import java.util.*;

class HolidayPlanner implements java.io.Serializable {
private String companyId;
private HashMap holidayRecords;

public HolidayPlanner(String companyId)
{
this.companyId =  companyId;
holidayRecords = new HashMap();
}

public void addHolidayRecord( HolidayRecord h)
{
String emp = h.getEmployeeID();
holidayRecords.put(emp,h);
}

public void removeHolidayRecord(String employeeID)
{

holidayRecords.remove(employeeID);
}

public HolidayRecord getHolidayRecord(String employeeID)
{
return (HolidayRecord)holidayRecords.get(employeeID);
}

public String toString()

{
return "  Collection for   " +  companyId + " :\n  " + holidayRecords;
}
}

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import java.util.*;
class HolidayPlannerTester
{
public static void main(String [] args)
{
HolidayPlanner p = new HolidayPlanner("8788");
HolidayRecord h1 = new HolidayRecord ("1",14);
p.addHolidayRecord(h1);
HolidayRecord h2 = new HolidayRecord ("2",14);
p.addHolidayRecord(h2);
HolidayRecord h3 = new HolidayRecord ("3",7);
p.addHolidayRecord(h3);
HolidayRecord h4 = new HolidayRecord ("4",10);
p.addHolidayRecord(h4);
HolidayRecord h5 = new HolidayRecord ("5",23);
p.addHolidayRecord(h5);
HolidayRecord h6 = new HolidayRecord ("6",7);
p.addHolidayRecord(h6);
HolidayRecord h7 = new HolidayRecord ("7",21);
p.addHolidayRecord(h7);
HolidayRecord h8 = new HolidayRecord ("8",23);
p.addHolidayRecord(h8);
System.out.println(p);
try {
ObjectFileUtility.saveObject(p, "HolidayPlanner.object");
System.out.println("Planner saved.");
}
catch (java.io.IOException e) {
System.out.println("Save failed. " + e.getMessage());
}
}
}