The 'msgina.dll' file is required during the login process because it is required for user authentication in the GUI mode. You have not mentioned the name of the security update you installed. That might have not been installed correctly. Right now you can try to restart the computer and press the [F8] key after the initial boot screen (memory test).

When the Advanced Startup Options appear, choose the "Last Known Good Configuration". You should reach the desktop since it will load a snapshot of the system when it had booted without any problem. For Windows XP users

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if "Last Known ... " does not work then try booting into the Safe Mode. Run System Restore from Start I Programs I Accessories I System Tools and select a date when the system is booted without any complication. XP will restart with the system snapshot created for the day you choose.

Download the security update again and save it to your hard drive. It is assumed over here that you tried to install a security update named "MS_Update. exe". Replace this name with the name of the security update. Enter the following command to install the update manually into a folder called "MyTemp" in the "C:" drive. Press [Enter] after giving the command, X:\MS_Update.exe /T:C:\MyTemp ("X" is the drive in which you save the security update prior to installing it manually.)