You are right.
I think you are problem might be caused by a missconfiguration on the firewall.
To test it quickly:
Add a rule to firewall->packet filter->filtering rules for traffic coming out from eBox
Add a rule to allow everything there, save changes and take a look at the openVPN logs under /var/log/openvpn
I did what you told me, althrough I don't have the Firewall module activated. After that, I've recreated the OpenVPN Client, clicked Create, then save changes, then save... It gives me an error (it always does when creating OpenVPN Clients, I supose due to the fact that there is only one NIC) saying that the changes to the modules below were not saved, but there is no module below, and I've checked the config of the client (both via eBox portal and viewing the files via ssh) and everything is there. The connection is also showed in the status screen, althrough with vpn interface status "No active". I will try to test this again with another NIC during next week, but I really just wanted to use one card....
PS: If I run the openvpn command with a costum .ovpn/.conf file via ssh, I can get connected, but still, I wanted to use the eBox interface for this...
PS2: About the tun/tap thing... Is there a way to use tun insted of tap, or to tune the configuration of the client (thing like tun, lzo, etc etc etc...)
Thanks for your attention