Internal Server Error after first reboot

Trying to install grommunio with the latest ISO on my Proxmox.

Installation seems to be working fine, and so is the server (both admin and users can log in).

But after the first reboot, I get "Internal Server Error" when logging in to admin interface on port 8443.

What am I doing wrong here?

Könnte auch das sein

Wow - strong community here. Thanks a lot guys! (Need to work a bit on my German ;-)

So - I've been changing one thing during installation and been over it a million times now.

I seems that if I don't change/set the system password, i works fine. Even after reboot.