Xu Cui

How to get a cert in the first place:

http://www.adobe.com/devnet/air/articles/signing_air_applications_print.html

If you encounter this error when signing your AIR application, do the following:

1. Download the Thawte Code Signing CA from www.thawte.com/roots
2. Extract the contents and find file “Thawte Code Signing CA.cer” in folder Thawte Roots\Thawte Code Signing\Code Signing CA\
3. Open “Internet Option” from control panel, click tab Content, then Certificate, then Intermediate Certification Authority. Then click on “Import certificate” button and import “Thawte Code Signing CA.cer”
4. Now go back to your original p12 certificate file. Double click and import your system (be sure to enter your password). Check the option “Mark this key as exportable”
5. After importing, go to Internet Options > Content > Certificates
6. Select your certificate and click export
7. Next
8. Yes, export the private key
9. Format: PKCS, (checked) Include all certificates in the… , (checked) Enable Strong protection, (unchecked) Delete the private key …
10. Next
11. Enter Password for the certificate
12. Next enter filename and export the file

It should be good.

Reference:

http://forums.adobe.com/thread/433530