VirtualBox only works once after Reboot

[jan-peter@ruehmann.name]

Hello
I have the following problem
with the old 5.0.24 everything worked fine, but after updating to 5.1.6 VirtualBox only runs once after Rebooting the System.
I am using Kubuntu 16.04 LTS
If I try to Start it a second Time a black window opens after a time a little window opens to with the Text "starting Virtual Machine" opens, next some Minutes later a third Window opens which says Starting Virtual Machine 2/2 opens goes up to 20% and then nothing happens.
There are no errors or messages, not on the Terminal too.
Killing all VirtualBox Programms and services wont help.
Only a complete reboot makes it work for one time again.
How can I make the actual Version work?

[socratis]

Please read the following: Minimum information needed for assistance.

For the VM log file ("VBox.log.zip"), here's what you do:

1. Start the VM. Not from a saved or suspended state. Clean start.
2. Take the steps required to generate/observe the error.
3. Shut down the VM (if it hasn't aborted by itself). Not suspended, not paused. Complete shut down. If you can't shut it down by normal means, close the VM window and select "Power off".
4. Right-click on the VM in the VirtualBox Manager. Select "Show Log..."
5. Save it (just the first log), ZIP it and attach it in your response (see the "Upload attachment" at the bottom of the form).

[jan-peter@ruehmann.name]

Hello thanks for the Answer.
Here is the Log File.
Seems the Pulse Backend is broken is Broken since after change to null everything is working fine.
The Network too.
Thanks,

[socratis]

I think you might be right on. The log finishes just about when the initialization of the audio happens:

00:00:01.051604 Audio: Initializing PulseAudio driver
00:00:01.061383 Audio: Initializing VRDE driver
Log ends here...

I'm not on a Linux host, so I don't know what your audio options are. You could also try one of the latest test builds which have been addressing some audio issues, AFAIK: https://www.virtualbox.org/wiki/Testbuilds