Hi,
seeing the same here. An:
apt-key list
shows that the key expired:
pub 2048R/E158C569 2011-08-03 [expired: 2014-08-02]
uid Samuli Seppänen (OpenVPN Technologies, Inc) <samuli@openvpn.net>
Deleting the key with:
apt-key del E158C569
and reimporting it via:
wget -O - https://swupdate.openvpn.net/repos/repo-public.gpg|apt-key add -
still shows that the key expired.