Hello,
I have a Lenovo Thinkpad p50. I connect it to my Dell Monitor at work using USB and the mini display port. When I unplug it out to take it back home and then open the laptop lid Ubuntu kills all applications and prints out some lines related to Bluetooth on a blank screen like this:

Bluetooth: hci0: Reading Intel version information failed (-19)
Bluetooth: hci0: Setting Intel event mask failed (-16)

I log in and all my applications are dead and I get a message from Ubuntu that it encountered a system problem with a button to report it. How do I fix this problem?

Are you suspending or hibernating the machine first before or after disconnecting from the DP? I can imagine that the X-server might get confused when waking to a different display configuration...