after updating, Virtualmin login screen comes up, but after authentication only an empty white page appears.
Already restarted (/etc/webmin/restart) and also reloaded (/etc/webmin/reload)webmin but still same thing.
What could I try next before loading backup?
How much memory does your box have? Is it a virtualized system (particularly vserver, OpenVZ, or Virtuozzo)? This sounds like maybe Webmin’s child process is dying before being able to serve a request, possibly due to memory allocation problems.
Absolutely right, I ran into memory problems again.
I searched for this:
… and it was my solution. This is a really good howto. Somehow the preload line was in the miniserv.conf again. Also proftpd was running again… So I run through the howto and now it works again.