Cannot access remote repository via SSH (Permission denied (publickey))

Question

I changed the laptop and now wWhen I try to do git clone git@... (using SSH), I get the following error message:

Cloning into 'test'... Permission denied (publickey). fatal: Could not read from remote repository.

Please make sure you have the correct access rights and the repository exists.

I did the following steps. Since I was able to clone the repository from my old laptop, I decided to copy-paste the content of ~/.ssh from that old laptop to the new one. I only deleted the file known_hosts. In the folder ~/.ssh, I have the file config:

Host server2 
Hostname xxxxxx 
User xxxxx
IdentityFile "~/.ssh/id_rsa"

I have also id_rsa and id_rsa.pub. This is the same content as the one I had on my old laptop.

So, I don't understand the origin of the problem. Is there any issue with my settings or should I contact the agministrator of repository?

UPDATE:

This is what I get when typing ssh -vT git@gitlab.test.org:

OpenSSH_7.2p2 Ubuntu-4ubuntu1, OpenSSL 1.0.2g-fips  1 Mar 2016
debug1: Reading configuration data /home/user/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to gitlab.test.org [42.12.212.10] port 22.
debug1: Connection established.
debug1: identity file /home/user/.ssh/id_rsa type 1
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/user/.ssh/id_ed25519-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.2p2 Ubuntu-4ubuntu1
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.6.1p1 Ubuntu-2ubuntu2.4
debug1: match: OpenSSH_6.6.1p1 Ubuntu-2ubuntu2.4 pat OpenSSH_6.6.1* compat 0x04000000
debug1: Authenticating to gitlab.test.org:22 as 'git'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256@libssh.org
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 
SHA256:ttfy7K7NFEj913pHVx3lG4
debug1: Host 'gitlab.test.org' is known and matches the ECDSA host key.
debug1: Found key in /home/user/.ssh/known_hosts:1
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /home/user/.ssh/id_rsa
debug1: Authentications that can continue: publickey
debug1: Trying private key: /home/user/.ssh/id_dsa
debug1: Trying private key: /home/user/.ssh/id_ecdsa
debug1: Trying private key: /home/user/.ssh/id_ed25519
debug1: No more authentication methods to try.
Permission denied (publickey).

Answer 1

I solved the problem by running chmod 400 ~/.ssh/id_rsa.