Here’s the full error:
The Login User Interface DLL CSGina.dll failed to load. Contact your system administrator to replace the DLL, or restore the original DLL.

This happens when you uninstall, and sometimes install, the Cisco VPN client. Cisco VPN client adds a registry key that disables fast user switching and loads the client before booting into Windows.

The fix below requires editing your registry files. If you have no idea what a registry file is, you probably shouldn’t be editing them. If you edit incorrectly your computer may refuse to boot. Here’s the quick fix:

1.) Reboot the machine
2.) Press F8 to load up the boot options menu for Windows
3.) Select Safe Mode and then select your Windows Installation
4.) After Windows loads into safe mode, it’ll ask if you want to continue working in Safe Mode. Select Yes.
5.) Start >> Run >> “regedit” (without the quotes). Press Enter.
6.) Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\WindowsNT\CurrentVersion\Winlogon
7.) Look for the GinaDLL Key
8.) Select and delete this key. DO NOT delete the entire Winlogon folder of keys.
9.) Close Regedit and reboot the machine

***EDIT***
This is actually the most popular post on it.thelibrarie.com! Awesome!