Decompiling BSP maps with File Packing
If you want decompile for example cs_agency or de_dust2 in Counter-Strike: Global Offensive maybe you haven't any materials and have error models. It's because materials and models are packing in BSP maps.
How to edit maps with File Packing
Use BSPSource in the tab "other" set tick in in "Extract embedded files". Then put downloaded files and folders in game derictory. Done.