dbus error

[bigwheel]

Following error happened.

root@instance-5:~/ # java -jar skypeslackrelay-assembly-1.0.jar                                                         

** (process:2498): CRITICAL **: dbus_g_proxy_new_for_name: assertion 'connection != NULL' failed

** (process:2498): CRITICAL **: dbus_g_connection_register_g_object: assertion 'connection != NULL' failed
Exception in thread "main" java.lang.InternalError: Failed to connect to skype
        at com.skype.connector.linux.SkypeFramework.setup0(Native Method)
        at com.skype.connector.linux.SkypeFramework.init(SkypeFramework.java:60)
        at com.skype.connector.linux.LinuxConnector.initializeImpl(LinuxConnector.java:82)
        at com.skype.connector.Connector.initialize(Connector.java:489)
        at com.skype.connector.Connector.connect(Connector.java:437)
        at com.skype.connector.Connector.assureAttached(Connector.java:1021)
        at com.skype.connector.Connector.execute(Connector.java:940)
        at com.skype.connector.Connector.execute(Connector.java:897)
        at com.skype.connector.Connector.execute(Connector.java:863)
        at com.skype.connector.Connector.execute(Connector.java:822)
        at com.skype.Skype.getAllChats(Skype.java:784)
        at com.skype.Skype.getAllChats(Skype.java:713)
        at Main$$anon$1.<init>(Main.scala:13)
        at Main$.main(Main.scala:10)
        at Main.main(Main.scala)

• OS: ubuntu 15.04/14.04 64bit Server
• Env: VirtualBox/Google Compute Engine

My jar works correctly in ubuntu desktop(even in Virtualbox VM).
Then first I guess this is caused by lacking of library.
However, my jar still didnt worked correctly after I install all packages of Ubuntu Desktop to Ubuntu Server.
Finally I gave up.
Plz tell me solution anyone.

P.S.

Skype4Py works correctly in same envirionment.

PSPS

It works correctly with -Dskype.api.impl=x11.
I decide to use x11 mode.