RHEL 9 Boot Error -[ end Kernel] panic - not syncing: Attempting to kill init! exit ..

I have installed RHEL 9 for testing and evaluation purposes on Oracle Virtual Box 6.1. The installation was successful, and I even successfully enabled the subscription. The system was running fine, and I was using it without any issues. But suddenly, two or three weeks later, when I tried to boot the system, it gave me the following error.

[ end Kernel] panic - not syncing: Attempting to kill init! exit ..

I even tried to install a fresh new Red Hat 9 on Virtual Box 6.1 and got the same error. Any advice is highly appreciated. Thanks!