CS:Source v34 or OrangeBox Server ?
The error comes because source engine has a limit of number of entities that can exist on a map at a time. The limit is 2048 entities. Since the map is so big, you are very likely to exceed the limit. Once the limit is reached the server (or maybe client as well) will crash and all the players will get that error.
Such big maps are not meant for public server as they have huge number of edicts or entities. You can try to use a Metamod/Sourcemod plugin to keep a check on the entities. These plugins will generally remove unused entities from the map. But if the map still has too many entities, then plugins will not work either. In that case, you will have to remove the map from map pool.