Problem using S/MIME in kmail

Dear users,

I am running a current version of kontact 5.11.3 with kmail included from 
Archlinux. Since some time I have the problem, that I can no longer send mails 
of save them as draft if the message is to be encrypted or signed using S/
MIME.

I get the message
> Could not compose message: Server indicated a failure

Disabling signature and encryption lets me send/save the message.

Does anyone have similar effects or an idea where I can look in order to track 
this down?

Thanks
Christian