With seahorse I have created a new key for me of the type PGP key (for email encryption)

I verified it by checking properties of that key. It exists, is signed, has the right date, ...

Now I go to Thunderbird 17.07 on my AMD/64 machine and open Keymanagement under OpenPGP. No key is available!
I check the directory .gnupg and find an update of the pubring and secring according to the time I made the key.

I try to send a message to myself and get:
Send operation aborted.
Error - encryption command failed

What do I miss?