Debugging Server connection interrupted messages
I had the same problem and wrote this post with the answer:
The fix is to remove/disable /System/Library/LoginPlugins/FSDisconnect.loginPlugin
The following steps should sort you out:

Click on the spotlight icon (magnifying glass) in the upper right of your screen

Type in ‘terminal’

Click the ‘Terminal’ icon (black with white border) under applications

Type in the following command (and hit enter):
sudo mv /System/Library/LoginPlugins/FSDisconnect.loginPlugin /System/

It will prompt you for your user password. Type it and hit enter again

Reboot


This just moves the plugin to /System so you can restore it again if needed by replacing step #4 with sudo mv /System/FSDisconnect.loginPlugin /System/Library/LoginPlugins/.