MQTT mosquitto TLS Issue

I have my all-in-one hass on raspberry pi 2 setup for 3 weeks, i initially setup mqtt with ownTracks and all worked fine, i am trying to setup TLS for mosquitto and can’t get it to work. Is this becaz of the mqtt server that already comes with hass or some other issue i don’t know.

I generated the certificate (followed this instruction OwnTracks and Mosquitto Private Broker with TLS)

I see in the mosquitto.log
Error: Unable to load server key file, check key file.

I set permission to all the cert files and it still give the error.

Any help would be appreciated.