and PPTP connection to VPN

I notice that when I’m connected to a VPN via PPTP, I can’t get use at all. It just times out. As soon as a I disable the Comodo Firewall, it works fine. Other smtp services work okay with the firewall enabled.

I now see that if I uncheck “Block fragmented IP Datagrams” works okay. How important is it to have the protection checked?

It is blocking these alerts as there are most of the time only relevant for routers. But experience learns that in big LANs like from universities or corporations it needs to be switched off to get the connection working.