[Evolution] Signing e-mails with gpg fails

[Rock Storm <rockstorm gmx com>]

Hi everyone and thanks in advance,

I'm not sure why but I am currently unable to sign e-mails, I'm getting
the following error:

    Could not create message.

    Because "gpg: skipped "67449612": No secret key
    gpg: signing failed: No secret key
    ", you may need to select different mail options.

I believe signing works and the secret subkey is "find-able" because I
am actually able to do the following without any errors, and this is
why I don't understand the error given by Evolution:

    $ gpg --output random.sig --detach-sig random.txt

    You need a passphrase to unlock the secret key for
    user: "Rock Storm <    rockstorm gmx com    >"
    4096-bit RSA key, ID 67449612, created 2016-02-21 (main key ID
    C96832FD)

    $ gpg --verify random.sig random.txt
    gpg: Signature made Sun 28 Feb 2016 11:47:47 AM CET using RSA key ID
    67449612
    gpg: Good signature from "Rock Storm <    rockstorm gmx com>"

I am using Evolution 3.18.5, GnuPG 1.4.20, Gnome 3.18.2 and Debian Sid
64bit.

Thanks again,
Regards,

Rock