For starters, this error came up after the last Counter Strike Global Offensive update on 2020.05.04. To reassure everyone, your account is not banned or anything like that. What may be happening is a conflict between certain files from the old version with the new one.

• It is important to note that it is not the same error as pak01_001.vpk

• A message like this must appear, it may vary according to your language

For many players, this fix works perfectly for them without the need to reinstall the game.
Keep in mind that the route may be different depending on where you have steam installed.

1. Close all Steam Services & Client
   
2. Go to: C:\Program Files\Steam\userdata\xxxxx\730\local\cfg
   
3. Back up the file and delete it
   
4. Go to Counter Strike local files
   
5. Open folder "csgo"
   
6. Delete folder "materials"
   
7. Delete folder "models"
   
8. Open Steam on "Disconnected mode"
   
9. Open Counter Strike & change to connected mode
   
10. Try first in casual mode.
    
11. If it works, try on MM.
    
12. Now you can back up the cfg file.

1. Close Counter Strike
   
2. Do a file integrity check A warning has to come out that a file could not be verified
   
3. Now try redoing the first solution

1. Delete Counter Strike
   
2. Go to your "steamapps" folder
   
3. Go to "common"
   
4. Delete folder Counter Strike Global Offensive
   
5. Install Counter Strike again

You can also go back to a beta version and then to the new version

Your identifier is after partner= and it is a set of numbers