Internal server error on node save
This was most likely caused by a rather long script that was timing out. The IPCCommTimeout on your virtual server is set to 40 seconds. If you encounter this problem again, you could edit the Apache directives that apply to this virtual server in /etc/apache2/sites-available/test.com.conf and set IPCCommTimeout, for example, to 300.

If you are using Virtualmin


Chose the virtual server that you want to edit from the drop-down
menu
Go to Services -> Configure Website -> Edit Directives
Modify IPCCommTimeout from 40 to, for ex. 300 (seconds)