OpenVPN certificate removal and connecting with no certificate file on server

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http://serverfault.com – I've run into a problem, that I removed certificate files from the server. But client that has these files still can connect. I've found out, that I should revoke the certificate and that this can be done by changing line with that certificate in /etc/openvpn/easy-rsa/keys/index.txt to have R, not V, as first character line. But previously I've removed line for that certificate from the file, because attempt to generate that certificate again just gave an 0 byte size file. As I've read, it shouldn't be able to connect after removing from index.txt, but it does connect. What may caus (HowTos)