Minecraft server is in offline mode?

When I start my MC Server I get the following message:

[12:55:49 WARN]: The server will make no attempt to authenticate usernames. Beware.

[12:55:49 WARN]: While this makes the game possible to play without internet access, it also opens up the ability for hackers to connect with any username they choose.

[12:55:49 WARN]: To change this, set "online-mode" to "true" in the server.properties file.

And my friends can't join in my server.properties the online mode is set to true

I have released all the ports, the firewall, etc

But it still doesn't work

Do you have any plugins on it?

Yes pex worldedit worldguard and bed rel

And what version does the mc server have?

It runs on the bukkit version 1.8

Is it a BungeeCord server or single server?