I had the same issue on jailbreak ! At first , I thought it was dproto fucking up and recognising me as a fake non-steam player and banning me afterwards ( when I try to reconnect ) , but seeing that it happened to me only on Jailbreak , I doubted that someone would have really changed something in dproto for JB !
This error can also happen if you have a bad connection , and seeing as I have god-like internet broadband , I thought that this wouldn't be the case , but then I thought it maybe the server not getting any data from the client , thus I concluded it may be a problem from the port !
So I went to my CS launch options but right clicking on the game library then choosing Properties and Set launch options and added this in the box : +clientport 27006
I tried joining after wards and it worked and I didn't get any error

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Of course if you are banned currently you can't join , since dproto banned your ip by default for 120 mins , so you need to hold for 2 hours until you try it out !
If it works for you as well , please let me know as a lot of players are having the same issue in some servers

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Cheers.