Some of us experience message from picture. After google it, try find fix, and ask community for help, much effort was needed to fix, and almost nothing works.

Situation 1 : player play in server, lost connection to server, try connect again, and after some time got message - Connection failed after 10 retries.
After testing, is possible to connect to any other server, only not in server where error occurred.

Situation 2: Player cant go online with game, try connecting to any server and got message Connection failed after 10 retries. Player may open web browser, download data etc.

In that situation, stuff which one don't help, and others try recommended are:

- verify integrity of game cache
- restart game, PC or steam
-reinstall game
- playing with options of firewall and antivirus

Player is connected to server where play trough port of IP address. In some situation, port may become bugged, and not response. Port looks like occupied in side of client or server, and is not available.
What is port? Port is one string between your PC (client) and server. One port may be used for mail incoming, other for mail outgoing, second for mozilla, other for one online game one server, like lot of nets.
For other people on server, you look like you are frozen, and leave game. Other players dont have any issues, only you.

When you try connect, fail is because port dont have propper information of last disconnection, and think is allready connected, and cant connect again. How long you have same IP, and use same port, that bugged information stay and prevent from connectin to server.

problem is not in your PC, game or something else, it is issue from ISP ( internet service provider) and fix for that is easy.

Here is 2 solutions for this issue:

1) more easy way - turn off router. After router restart, automatically obtain new dynamic IP address from providers pool of IPs. That address have refreshed ports, ready to do their tasks. If player are confused - i dont have dynamic IP, because is same half year, reason is: or you pay for static IP to your provider, or you have good provider who give it for free, or you got same right on same IP after rebooting router.
Resetting router send information to provider -im off. After turning on, similar info is sent to provider, and automatic default is to start protocol - connecting user, and obtain new fresh IP.

update for reset router: to be sure to obtain fresh IP, try turn off router longer than 3 min. Reason is - sending info to provider - you are off, later when connect after 3 minutes, provider treat you as new connection


2) wait couple days to problem solve by itself. How this is possible? Easy: provider reset every couple days your IP to prevent problems, and after ( regular in some countries is 3 days) some time u will get new IP.

3) Player may change gaming port manually.

step 1: open steam, library, right click on left4dead2, select properties















step 2: in opened window select - SET LAUNCH OPTIONS
















step 3: in opened window write command - +clientport 270XX

Important! XX - instead of XX-es write any numbers between 05 and 32 (exclude 20)













RESTART GAME!!!

what really u do? Game may use ports for play - 27005, 27006, 27007...27019, 27021,27022,27023,27024...27032.

By default may be using port 27005 ( that is maybe your bugged port ) so must change it to another one that works.

examples: +clientport 27027 +clientport 27019 +clientport 27031 +clientport 27008 etc.


Final conclusion: This maybe cant help for some players. If that so, that players have static IP. If u have static IP, and nothing help you, u must call ISP (provider) contact center, and say - hello, i got issue with my internet, cant play online games, but i may search internet, youtube etc. Plese give me new IP address.

Edit #2: IP address which one causes trouble ( blocked faulty port) is Public IP ( between provider and world) , not local IP ( between router and provider)

Edit#4 : for people who use static IP (in some countries need pay extra for it) is hard to fix, so i suggest to try play from same router with other machine ( laptop, other pc etc).

edit#5 : Delete Helms deep reborn custom map from workshop subscriptions, because map change UI, removing some menu items. If removing not help, use guide to FIX that using this steam guide:
https://steamoss.com/sharedfiles/filedetails/?id=1595194095&searchtext=helms+deep

Edit#6 : the Last Stand major update dont have anything with that error because way of connection to game is same as before

Edit#3 : u may found interesting my other steam guides:

http://steamoss.com/sharedfiles/filedetails/?id=687890226
http://steamoss.com/sharedfiles/filedetails/?id=760513810
http://steamoss.com/sharedfiles/filedetails/?id=690930421