When renewing a certicate, sometimes we lost our private key, to avoid this you should backup your private key after the renewing certificate process.

Here is step by step backup on Microsoft IIS 6.0

1. Start > run > MMC you will see this kind window apear

2. Go into the Console Tab > 'File' > 'Add/Remove Snap-in'
3. Click on 'Add' > Click on 'Certificates' and click on 'Add'

4. Choose 'Computer Account'

5. Choose 'Local Computer'

6. Close the 'Add Standalone Snap-in' window.

7. Click on 'OK' at the 'Add/Remove Snap-in' window. you will see this on your mmc

8. Open up the 'Certificates' Console Tree
9. Look for a folder called 'Certificate Enrollment Requests' > 'Certificates'

10. Select the file that you wish to back up.
11. Right-click on the file and choose > ALL TASKS > Export

12. The "Certificate Export Wizard" will start up. Click on 'Next'
13. Choose "Yes, export the private key". Click on 'Next'.

14. Leave the default settings and click on 'Next'

15. Enter your password to access the file.

16.Choose to save the file to a set location.

Type the key name in the 'File Name' box, and click 'Save'.
Click on 'Next'

The file is given a *.pfx file-name extension and should be saved to a 3 1/2" disk on the a: drive or your hard disk drive.
It is important to make a copy of the Private Key that does not reside on the actual server; in the event that the server crashes.

17. Click 'Finish'
18. You will receive a message that states "The export was successful" when the export has been completed. Click on 'Ok'

Thats all Folks ^____^