Applet simply disappear after some hours working

Hi everybody,
I'm getting crazy with a Java Applet that simply disappear after some time (usually hours, sometimes minutes) of usage.
Applet loads properly and runs. During execution, it contacts a server by invoking servlets and also is listening on a RMI port.

Since some times (probably starting from 18/4/2012, when we started to upgrade all our 900 clients to Oracle JRE 1.6.0_18) the applet simply disappears on its own: this may happen while the user is interacting with it, but also when it is idle.

The clients are running WinXP SP3, IE 7, and as said JRE 1.6.0_18. We already tried to upgrade to 1.6.0_31, or to move to IE8, and to disable the "next generation plugin" setting. Nothing, the applet still randomly disappear.

No hs_err_pid files are generated. Application logs does not report nothing strange, they simply stop. In most cases, but not always, the browser closes when the applet disappear. Nothing on the Windows event viewer. Any idea?

Is this a Java applet that you yourself have created?

Cross posted
Applet simply disappear after some hours working (Applets forum at JavaRanch)

Also did both start a thread and resurrect a zombie on that site.

db

@Fubarable:
I did not created the Applet by myself, but I can get in touch with the developers
@DarrylBurke
I was not aware that posting the same question on separated forums is considered cross posting