Try to set
Code:
max_entities
in main function. Before spawning ents at runtime and before level load this var must be set.
Default set is 10times your nexus.

I had this prob with grass models placed via seed map. So i set this var and all was fine. I used 30.000ents for testing, now around 12.000 grass models.

edit:
Guess u guys talking only about "hand-placed" models in WED / map editors. I was talking about runtime creation. So my post wont help much laugh

Greets

Acknex umgibt uns...zwischen Dir, mir, dem Stein dort...
"Hey Griswold ... where u gonna put a tree that big ?"
1998 i married my loved wife ... Sheeva from Mortal Kombat, not Evil-Lyn as might have been expected
rayp.flags |= UNTOUCHABLE;