I'm actually surprised I haven't seen this posted yet.
What are Edicts?
Edicts are slots for entities. If too many entities are spawned and the limit has been reached, the server will crash with the Error message "No free edicts".
How did this fix become avaliable?
Somewhen in 2004 the Valve Developer Alfred Reynold added a command line to HL 1 which allows to increase the default amount of edicts from 900 to anything you want! The problem is, that noone got ever informed about it.
So how do I fix it anyway?
You set it up like this: -> Steam Games List -> Right click on any goldsource modification -> Properties -> Set launch options -> Write "-num_edicts 2047" there, without the quotes. The number may vary. -> Close both windows with the Ok button -> Start your game and spam entities