ubuntu - Getting “Server unexpectedly closed network connection”

I created VM by using Jclouds API and by giving the public address in putty login into the VM. I tried to install GUI in VM by giving the below command

sudo apt-get install ubuntu-desktop 

It is installed but, while rebooting the Ubuntu server I am losing internet connection getting message like below:

sudo reboot

Server unexpectedly closed network connection

Then the server won't respond.