Error when creating a mirror partner in SQL 2014

i'm creating a mirror feature on my server. first, I created he Main partner targeting the mirror parthner and it worked ok.

But, when I try to create the mirror partner to Main server ( mirror --> main) , it doesn't work and return the following error: 

"The server network address "TCP://PC-DEV-82:5300" can not be reached or does not exist.Check the network address name and that the ports for the local and remote endpoints are operational."

I've tried the follow tutorial but I was not successful.

http://blog.sqlauthority.com/2010/01/11/the-server-network-address-tcpsqlserver5023-can-not-be-reached-or-does-not-exist-check-the-network-address-name-and-that-the-ports-for-the-local-and-remote-endpoints-are-operational-microso/

Could you please help me or drive me to another tutorial?

Thanks in advance.

Luciano