I generated server.csr using openssl CLI and then generated server.key from that
You're supposed to generate a private key first:
openssl genrsa -des3 -out server.key 1024
then generate a csr:
openssl req -new -key server.key -out server.csr
If you're requesting a new certificate, you then send the CSR to the CA. It sounds like what you have is a CA certificate, not a server certificate.