Quote by der nette Mann :
everything fine today
no more connection problems

Hi der nette Mann, sorry for late response.

This error can be caused either by the server or steam client.Previously cs1.6 runed on p47 dproto protocol,
quite some years ago the migration was done to p48 version.
The utility of this is to let noSteam users(some hack'd(free) clients), play with p48 steam clients.

This happens many times to me, if your game crashes, and try to rejoin sometimes you are registered as p48 client but
since your steam verification c ant be handled server thinks that your trying to access with a STEAM_LAN_ID p48 client version, which is prohibited by dproto.
To solve the issue if its client side error: Just restart your whole steam client, and try to rejoin.
If error persist its a server-side, which restricts the entrance of steam users, can be solve with server restart(this happened before on fun maps), the work around this one is to join server with nosteam client which has p47.

.hf happy
 

                                                                
                                                                
   ^!.    .^^~~~~!!!77!!!??7777777777777777~                    
  .!7!~~~!?J!77!!!!77?7??JJ?JY55Y5555PPPPP55?!~^:::^~^:..       
      .......  .  ......::::^^!???777!!7JYYJ77777JYPGGGPP55Y7.  
                              ~77!:.: ..:!7~   ..:^!7?JJYYYY!.  
                            :!7!!:       .7?!        ..:~!7!:   
                         .:~77!~:         :!!.            ...   
                         :77!~:.                                
                          .^.