Gregorian calendar gives a java.lang.IllegalArgumentException only on 12-31-00.
The exception arises even in jdk 1.3.0_01 and also jdk 1.2.2_06. 

TEST CASE FROM CUSTOMER
=======================
import java.util.*;

public class GregCalBug {
  protected GregorianCalendar gc;

  public void run() {
    int nYear;

    gc = new GregorianCalendar();
    gc.setLenient(false); /* Bug only manifest if lenient set false */
    try
    {
      gc.set(2001, 1, 1, 1, 0, 0);
      nYear = gc.get(Calendar.YEAR);
    }
    catch (Exception ex)
    {
      System.out.println("We should _not_ be here!");
      System.out.println(ex);
    }
  }

  public static void main(String[] args) {
    System.out.println("This small Java class demonstrates a bug in");
    System.out.println("Solaris JVM JDK 1.2.1_04");
    GregCalBug me = new GregCalBug();
    me.run();
  }
}

Output of the above test case  when date is set to 12-31-00.
smala:/home/mala2/gregorian 62 % java -fullversion
java full version "1.3.0_01"
smala:/home/mala2/gregorian 63 % javac GregCalBug.java 
smala:/home/mala2/gregorian 64 % java GregCalBug  
This small Java class demonstrates a bug in
Solaris JVM JDK 1.2.1_04
We should _not_ be here!
java.lang.IllegalArgumentException
smala:/home/mala2/gregorian 65 % 

Please call gc.clear() before gc.set() to clear the wrong value in time fields.

 xxxxx@xxxxx  2001-01-09

This bug is reproducible on December 31 in any leap year. (But not reproducible on 2001.12.31.)
 xxxxx@xxxxx  2001-01-09

Corrected the condition of checking the fields(DATE and DAY_OF_YEAR) validity.
 xxxxx@xxxxx  2001-01-15


This bug was fixed in 1.4 (beta) and 1.3.1_12.
 xxxxx@xxxxx  2004-12-24 02:02:11 GMT

doesn't occur in jdk1.3.1_06 while the related bug 4398844 
still occurs

used testcode:
Calendar cal = new GregorianCalendar();
cal.setLenient(false);
cal.set(1952, 11, 31, 0, 0, 0);
Assert.assertEquals(31, cal.get(Calendar.DAY_OF_MONTH));
Assert.assertEquals(11, cal.get(Calendar.MONTH));
Assert.assertEquals(1952, cal.get(Calendar.YEAR));
-> all the asserts returns true

This bug is also seen in jdk1.3.1_08

Here's what I did:
Calendar cal =   Calendar.getInstance();
cal.clear();
cal.set(1992, 12, 31);
cal.add(Calendar.YEAR,4);

I get an IllegalArgumentException at this point.