Credentials.acquireTGTFromCache (null, null) returns null using jre 7

I'm admittedly unfamiliar with the JAAS API, but you need help investigating the issue we encountered when upgrading to jre 7. Applications that previously had the ability to automatically log in using the current Windows username stop working. After some conversation, he comes to this line of code.

sun.security.krb5.Credentials.Credentials.acquireTGTFromCache(null, null);

This returns null when using jv7 jvm, but returns the correct curves when using jre 6. I wrote a test class in its simplest form and still see the same behavior, so it could not be related to the code in our own classes.

package test;

import sun.security.krb5.Credentials;

public class Scratch {
    public static void main(final String args[]) throws Exception {
        final Credentials yaoza = Credentials.acquireTGTFromCache(null, null);
        System.out.println(yaoza);
    }
}

? . !