A strange error in Sun's Krb5LoginModule for Java versions: 1.4.2_14, 1.4.2_15.
The problem does not exist in Java 1.4.2_13.
In order to support Kerberos authentication a SPNEGOLoginModule was implemented, which uses JGSS API. For Java version 1.4.2_14 and 1.4.2_15 (We didn't test any other versions, but it seems to have this problem after JDK 1.4.2_13) the method createCredential(...) throws a NullPointerException in Krb5LoginModule.
You can reproduce the problem by using attached sample application. Additionally it is attached a stack trace about the exception.