I am getting "Unknown Error = -2,147,414,007" on creating a certificate through the Keychain app.
Steps to Recreate:
Open the Keychain Access application. Select Certificate Assistant > Create a Certificate in the application menu (Keychain Access). Only Modified Parameters are listed. The remaining options are kept with default values.
Name of Certificate = gdbcert
Identity Type = Self Signed Root
Certificate Type = Code Signing
Check the Let me override defaults checkbox, and click Continue.
On the next page, leave Security Number to be 1, and set Validity Period to 3650.
Then click Continue once again, and keep doing so to skip the next six screens until you see the one entitled Specify a Location For The Certificate.
For the only property, Keychain, choose System from the drop-down list. Lastly, click Create, type in your password, if prompted, and click Done.
Update: I'm able to create certificates to the Login Keychain. The issue is only when I try to create certificates for the System Keychain.