I prefer to fix it instead refund :D
Actaully our lead developer is inspecting your issue, but since he prepared to release version 4.4 so will be delayed to debug this..

is not possible you change the server to apache ?

Nearest time when I can try to move server to appache - is the next summer. Untill that I rather prefer to work without groups than risk to get not working sites. I'm not professional sysadmin, I'm a teacher.
So I can wait more but note that I applied for refund within the 14-days period! :)

yeah please wait for it.. our developer will inspect it once the package 4.4 is ready..

well, please you change all files and folders permission to www data

What value should I set?

please look at this stackoverflow.com/questions/9133024/www-data-permissions

I can't understand from this article what permissions I should set for your purpose. Now there's default values set by joomla and components installers: 755 for directories and 640 for files. Tell me what values to set and I'll do.

Please check this
askubuntu.com/questions/378351/permissio...ownership-of-var-www

755 or 640 is chmod, you need use chown to change the onwer permission, try run this on your server terminal command

chown -R www-data:www-data /YOURWEBPATH/

You mean change owner? Why? If I change owner from exact server user to any else the server will not work. This user creates automaticaly when I create new site from control panel (I use ISPconfig).

"www-data" is default ownership, please try it.. it bit risky you need to know the current onwer, so you can revert it back if it doesnt work

No, it's not related to my system. Server users in my system have names like web6, web5, web1 and groups are client1, client2.

Hi,

Finally I able to fix this, this issue caused by database community_files is broken, field groupid was missing there..

Oh really it works! Thank you!
I'll be back if something else go wrong. :)

you're welcome :)