You have received an invalid certificate. (after generating a new one)

After generating a new cert for SMTP-TLS from within nodeworx (my previous cert had expired) I receive the following error message from Thunderbird when trying to send a message:

An error occurred during a connection to

You have received an invalid certificate. Please contact the server administrator or email correspondent and give them the following information:

Your certificate contains the same serial number as another certificate issued by the certificate authority. Please get a new certificate containing a unique serial number.

(Error code: sec_error_reused_issuer_and_serial)
I receive this error even after deleting Thunderbird’s cert database (cert8.db for the specific profile), which apparently is the proper way to refresh Thunderbird’s cert database. The error also occurred even before doing this.

Any ideas what may be causing this issue?

I figured this out and am posting again in case the solution is helpful to anyone else.

Instead of generating a new cert just for the one service, SMTP-TLS, I went and again generated a new cert but this time applied it to POP3-SSL, IMAP-SSL & SMTP-TLS… and now everything is working fine again.

Glad you got it figured out John!