Still strugling with the Lync client downloaded from the Store for Windows 8. You are not an VPN or useing UAG. Well hope you had installed the backward compability on the Lync 2013 server.
It's in the SETUP catalogue. It's named: OCSWMIBC.msi
If you are not sure that you have it installed, just download the BPA for 2013 you will find it here: