Shared printing is no longer working I run a Mac mini as a server in a small company. With macOS Server. Also a print server with a few shared printers.

This is the error message in the CUPS log: 

Unable to encrypt connection, internal error


Yesterday the macserver.local self signed certificate expired. So I renewed it. Restarted the Mac. Still the same error.

What I tried:


Restarting CUPS
Turning off Sharing Printers (in system preferences > sharing)
Changed trust settings of certificate in Keychain to Always
Removed shared printer and re-add it again
Everything suggested here: https://discussions.apple.com/thread/7610729 (excluding reinstalling macOS)


Still the same error. What is the solution for this problem?
If there is additional information required please let me know.

Cups error log:

E [11/Oct/2018:19:57:26 +0200] [Client 16] Unable to encrypt connection: Internal error


cupsd (security) in console:

CSSM Exception: -2147409622 CSSMERR_TP_NOT_TRUSTED
I believe this thread could be of benefit to you.
https://discussions.apple.com/thread/7610729

This sounds like an access/trust issue to the certificate. 
You can try changing the trust setting on the certificate within Keychain>Doubble Click on certificate>Trust>Always Trust

If not, the CUPS logs could be beneficial to narrow down the issue