How to fix "Could not open a connection to your authentication agent." problem in Ubuntu

First you have to find out what is your groupname of current logged in user. For example my current logged in username is arman. So I run following command in my terminal

id arman

Output would be something like below

uid=1000(arman) gid=1000(arman) groups=1000(arman),4(adm),20(dialout),24(cdrom),46(plugdev),105(lpadmin),119(admin),122(sambashare)

So my username is arman and groupname is arman

Step 1: Backup your ~/.ssh folder

Step 2: Run following commands in your terminal

sudo chown -R username:groupname ~/.ssh
chown username ~/.ssh
cd ~/.ssh
chmod 600 *

Step 3: Run following command in your terminal

exec ssh-agent bash
sudo ssh-add ~/.ssh/id_rsa