Server disconnects

Hi all,

brand new here - trying to eval the NG firewall

so far all is good but seems that server periodically disconnects

i have it set up as a def gway for a few clients and i have the AD integration installed (trial mode)

clients can browse internet anad i see traffic go through with username - then server goes offline

The console says
The connection to the server has been lost. Press OK to return to the login page.

server cannot be logged into at this point

phisical server is still there - did not reboot
after a few minutes all is back to normal but the ad usernames are cleared and firewall traffic is logged with no username


What would cause the firewall to go offline like this?