App Nap was released with Mac OS X 10.9 as an energy saver. Apps which are not in use will go to sleep. You should always disable App Nap on a Mac server that hosts the 4D server. You can disable App Nap for each application or for your entire computer, including background tasks.
To do that, use the following terminal command:
defaults write NSGlobalDomain NSAppSleepDisabled -bool YES