How to Stop the C000021a Fatal System Error the Session Manager

A C000021A fatal system error typically occurs when a service pack fails to install on your computer. It may also take place because of a third-party program that is not compatible with your system. Either way, you can fix this error by restoring your system to a last known good configuration. Note that you may need administrative privileges to perform this task.

• 1

  Click the Start menu and select "Shut Down."

• 2

  Click the option "Restart" and select "OK."

• 3

  Press the "F8" key to launch the Boot menu.

• 4

  Use the arrow keys to choose and highlight "Last Known Good Configuration." Press the "Enter" key.

• 5

  Use the arrow keys to choose and highlight your operating system. Press the "Enter" key to reboot your computer.