The error occurs when the game tries to park a car (load an asset) but the parking lot is full. The engine has a hard-coded limit.
The "State Pool" is a memory allocation system within the IW engine (the engine powering BO2). Think of it as a parking lot. When the game loads a map, textures, sound files, and player models, it parks them in this "State Pool" memory slots. The error occurs when the game tries to
Ironically, the problem gets worse on better hardware. When BO2 was released (2012), it was designed for 1GB–2GB VRAM cards and slow hard drives. Today, you have 8GB or 12GB GPUs and NVMe SSDs. The game sees all that extra memory, tries to fill the state pool with high-resolution textures and uncompressed assets, and hits a 32-bit memory ceiling much faster than it did a decade ago. Think of it as a parking lot