unable to encrypt emails in evolution using gpg

[edward torvalds]

When I encrypt email and click Send I get this error and sending mail
fails

Because "gpg: CEF41E5C: skipped: unusable public key
gpg: [stdin]: encryption failed: unusable public key
", you may need to select different mail options.

Where CEF41E5C is my key.
Please note: I have imported both private and public keys of mine. Also
the paraphrase I enter is correct

Please help, thanks.

-- 
edward torvalds <ltorvalds024 at gmail.com>