Hello,
After my actual OMV 4.x-installation was not able to find the ethernet interfaces of my HP Proliant Microserver gen8 anymore, I decided to install a freshly OMV 4 from USB to a new SSD-System-Disk.
Installation was no problem. The installation was able to find the ethernet interfaces.
But, at the end of booting the system-ssd, this error message occurs and the WebGUI does not start: