Unable to sign email

I was sending an email, when my keyboard suddenly died, and I was unable to 
enter the pass-phrase for signing it, and had to cancel. Since then I've 
been unable to sign (and encrypt) email. I just get two popups saying "Could 
not compose message: No passphrase given", but no possibility to actually 
sign it.
I tried first logging out and in again, to no avail. Then I rebooted, but 
still the same.

I've been privileged that it has worked for years without problems, and now 
I haven't got the faintest idea how to get it to work again. It seems very 
fragile to stop working for such a little thing.
-- 

/Thomas