Steps to fix this error on code signing adobe air using .p12 cert from Digicert - Unable to build a valid certificate chain for the signer
a. Open Firefox and browse to https://www.digicert.com/digicert-root-certificates.htm
b. On the middle of the page, download -
|DigiCert Assured ID Code Signing CA-1||Valid until: 10/Feb/2026|
|Serial #: 07:F4:73:6F:AF:EF:40:8A:1F:66:40:F2:65:D1:0A:C1|
c. Install the cert in Firefox
d. Once done, export again the code signing cert from digicert, through (click Firefox -> Preferences -> View Certificates -> HIghlight the digicert code signing cert -> click Backup)
e. Done, the newly exported file should now have the valid certificate chain and that should fix the error "Unable to build a valid certificate chain for the signer"
Even though this is from Digicert, this should also work for other Certificate Authority providers assuming you download your provider's root cert for code signing.
Reigner S. Yrastorza