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." Pressione a tecla "Enter". Press the "Enter" key.

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

6 Insert the Vista DVD into your computer. Restart the PC.

7 Press any key when prompted to boot from the DVD.

8 Select your language, keyboard and current settings from the onscreen menus.

9 Click "Repair your computer." Select the drive containing the Vista DVD and press "Next" to automatically search for the root cause of the C000021A Fatal System Error and repair it.