System cannot find file specifed error

This error appears when the map compile has failed due to an error, or the current game configuration is not set up correctly.

1. Check the error log in the Hammer Process Window to make sure there are no other errors that may have caused the compile to fail. If a compile fails, no .BSP file for the map is written, and the game will not launch correctly.
2. If there are no other compile errors, you can try to reset the Source SDK game configuration.
3. Sometimes it is because of Too many portal verts, check the writing line in the compile log.
   

Solution: Reduce this number by reducing portals, which can be done by tying world brushes to entities like func_detail.