Ubuntu – Permission denied (publickey) Amazon Linux aws

I have two instances running on my aws. I have the same keypair for both of them. I was using both instances for long time. but today I am getting an error on one instance while trying to login through terminal if I run this command.

ssh -i mypem.pem ec2-user@52.xx.xxx.xxx
Permission denied (publickey).

But If I try to login to other instance with the same pem file. It works and I can successfully login to it.

I have tried all the solutions

• Permission denied (publickey) when SSH Access to Amazon EC2 instance and
• Trying to SSH into an Amazon Ec2 instance – permission error

but nothing works for me

If I do

ssh -i mypem.pem ec2-user@52.xx.xxx.xxx -v

the result is:

OpenSSH_7.4p1, LibreSSL 2.5.0
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Connecting to 52.xx.xxx.xxx [52.xx.xxx.xxx] port 22.
debug1: Connection established.
debug1: key_load_public: No such file or directory
debug1: identity file mypem.pem type -1
debug1: key_load_public: No such file or directory
debug1: identity file mypem.pem-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.4
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.4
debug1: match: OpenSSH_7.4 pat OpenSSH* compat 0x04000000
debug1: Authenticating to 52.xx.xxx.xxx as 'ec2-user'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256
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: mykeyhere
debug1: Host '52.xx.xxx.xxx' is known and matches the ECDSA host key.
debug1: Found key in /Users/myusername/.ssh/known_hosts:6
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<rsa-sha2-256,rsa-sha2-512>
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /Users/myusername/.ssh/mypem.pem
debug1: Authentications that can continue: publickey
debug1: Trying private key: mypem.pem
debug1: Authentications that can continue: publickey
debug1: No more authentication methods to try.
Permission denied (publickey).

What I have tried

chmod 400 mypem.pem

I have also tried this

sudo ssh -i amazonec2.pem ec2-xxx-xxx-xxx-xxx.us-west 2.compute.amazonaws.com

Got this

Please login as the user "ec2-user" rather than the user "root"

then I did this

sudo ssh -i amazonec2.pem ec2-xxx-xxx-xxx-xxx.us-west-2.compute.amazonaws.com -l ec2-user

I got

Permission denied (publickey)

If I try to login to other instance with the same key. I can successfully login. Please help what actually went wrong here

Security Group on my instance is this: