VPN connection auto-closes after a while...is it because I'm using Free licenses?

IDK if it's because of some kind of limit with the Free licenses or what....but the VPN connection between me and any of the 2 PC's of a friend of mine auto-closes (with the typical dialog box of "This was a free session etc etc"...) at an arbitrary limit (sometimes after 3 minutes, sometimes after 10). Any ideas? At the very least I'd like to discard that it is a Free version limitation.

I've the Connection Timeout limit set to Disabled BTW. Thx in advance for your help