What OS you are using now? Windows Server 2003/2008 or 2008 R2?
Whether you have installed the Terminal server(RD Session Host server) or not?
According to your description, I understand that non-admin users logon the target server, then they get the error message "The previous system shutdown at <time> on <date> was unexpected". Please check the system properties>Advanced>Startup and Recovery to see if Automatically reboot is selected under SystemFailure. It sounds like your server is blue screening and it’s set to reboot automatically when it does. Please also check the event viewer to see if any event log relates to this issue, then you can post here. Thanks.
If it is a hardware issue, contact your administrator or computer hardware vendor for further assistance.
According to my previous experience, please check if any antivirus software led to this issue. You can disable or uninstall the 3rd security software/ Management Agent in the Windows Server to see whether same issue still exists.
Hope this helps.
Technology changes life……
there are 10 Windows 2008R2 SP1 with RD Session Host role. And Yes, the Server has a BSOD but this is a other story. The questetion is, can i disable the Message for non Administrators? Normal users do not need this information. The only ask stupid questions ;-)