From Valve Developer Community
While compiling or attempting to play it, your map has hit some sort of memory limit.
Almost anything can cause this error.
- A brush entity is too large. (most common)
- Not enough system RAM. At least 128 mb is recommended.
- Byproduct of a leaf saw into leaf error.
- File pathnames are too long.
- Too many textures/WAD files being used.
- The level is simply too large in general.
- Too many SKY faces on hidden brush faces in the level.
- (Compile) Get more system RAM.
- (Compile) Try using a third-party compile tool interface to compile your map, instead of the Run Map interface in Hammer. This will free up more system memory to allocate to your map compile.
- (Compile) Check for any overly large brush entities, such as large trigger_hurt entities.
- (In-game) Some rendering properties may cause the OpenGL or Direct3D renderer to crash. Try testing the map in the Software renderer.