with the ubuntu upgrade you probably went from openvpn 2.0 to 2.1 as well; if you are using scripts in your server config you'd need to add
script-security 2
(at a mininum) to make it work again. The 2.0 behaviour can be achieved using
script-security 3 system
if you do not use scripts at all then post your configs, so we can have a look.