In case you select an expired certificate for "Encrypt to others" you will initially see the correct error message “This certificate is expired” below the field with the expired certificate.

But if you then click in the next field (or tab to the certificate list button) the message will change to “No matching certificates or groups found”. It will not change back, either, if you again click into the field with the expired certificate.

Note: This occurs in Gpg4win 4.4.1 and in the 5.0 Betas. But in the latter versions we have made it difficult to select an expired certificate in the first place.