You specified that this message should be digitally signed, but the application either failed to find the signing certificate specified in your Mail & Newsgroup Account Settings, or the certificate has expired.
Sće podał, zo so tuta powěsć digitalnje signuje, ale nałoženje pak njemóžeše signowanski certifikat, podaty w kontowych nastajenjach, namakać pak certifikat je spadnył.