Cannot select S/MIME signing certificate

Hi

I finally figured out how to import my certificate - Kleopatra couldn't recognize 
it but doing it in the CLI worked.
Now I want to use it for signing my mails so I go to "Identities", select my 
identity and select "Cryptography". From there I select "S/MIME signing 
certificate" and I get a list with my certificate as the only one listed. I 
select it but the OK button is still grayed out. I try the "Start Certificate 
Manager" button and nothing changes. Hmm, alright Kleopatra is already 
running; I shut it down and click the button again - Kleopatra starts again, 
but the button is still gray and unselectable.
What to do?

-- 
Best Regards / Med venlig hilsen

Thomas Olsen