Hi@akhtar,
You're getting the following error because you've already executed the join command on your nodes. It created your /etc/kubernetes/pki/ca.crt file even though your node failed to join.
To get rid of this error, execute the "kubeadm reset" command on your node and execute then join command again. This will reset your cluster environment and then when you try joining the node again to the cluster, it will create all the files again.