found on mapcenter:
Believe it or not, the error is more related to entities, not models. You have two kinds of entities; brush entities and 'right-click' entities.
Brush entities :- A brush entity just that, an entity that is made with a brush or several brushes. For example, you draw a 'common/trigger' brush and then turn it into a trigger_multiple.
That's a brush entity. Other brush entities are trigger_push, func_trains, func_buttons, func_bobbing, func_pendulum, func_plat... you get the message.
Correct me if I'm wrong, but I think you're limited to 255 brush entities. If you exceed that amount, you'll get the 'MAX_SUBMODLES exceeded' error.
Keep in mind that you can make ONE brush entity out of SEVERAL brushes, and it only counts as one.
'Right-click' entities :- I don't know the technical name for these, but I call 'em 'right-click' entities. You right-click and create an entity without associating it with a brush.
For example, you right click somewhere on your map and select 'Target' > 'target_position'.
Some other examples are ammo items, weapon items, path_corner, target_speaker, target_give,
target_kill, misc_model, etc. I haven't hit the limit on these yet, and I've heard that there really isn't a
limit here (but I bet they're wrong). I'd guess the limit is probably around 1024 or something like that.
But on that note, you can only have 255 visible model entities in a single vis portal or strange things will happen...
You'll fire your weapon but you won't see projectiles or explosions, ammo/weapons/health items will
vanish before your eyes or simply never respawn yet you can walk over where it should have been and
receive the item, ...strange stuff.
If there's over 255 visible models, the ones created after model# 255 will not be drawn until some previous ones enter an unseen vis portal.
BOTTOM LINE: Reduce the number of 'brush' entities to something under 255 and your map will work again.
now it says 255, but i have like 300 and it still worked at times, so i dotn exacly know, but just get rid of unneed buttons and stuff like that and it should work