When a signed applet that has an expired certificate is cached in the Plug-in cache using the cache_version and cache_archive parameters. A "Java Plug-in Security warning" dialog is displayed with information about the CertificateExpiredException that the expired certificate generated. The user is asked by the dialog if they want to ignore this warning and proceed.
Regardless of how the user responds the same exception dialog is displayed, with the new dialog, once again regardless of how the user responds the dialog returns and ultimatley can only be dismissed by exiting the browser.
Note that if the Certificate is not in the local store, a security dialog pops up after the exception dialog is dismissed. This dialog is the usual grant or deny dialog and again whatever selection the user makes the exception dialog re-appears.