HTTP ERROR 500 java.lang.NoClassDefFoundError

HTTP ERROR 500 java.lang.NoClassDefFoundError: com/inductiveautomation/ignition/gateway/web/components/LaunchLink$Applet

The gateway is working, the designer is working, but unable to go to the gateway web page.
Restarted the gateway, no effect.

Any idea

Is this Ignition 7.9 or 8+ ? The latter has no support for applets.

I did choose ignition 7.9, just saw that the forum included 8.0.
So, it is 7.9. Sorry for the confusion.

Can you post the full error and stack trace somewhere or upload your logs?

Did you do an upgrade recently or something like that?