Peerblock is a widely used software - It essentially blocks known bad IPs from connecting to your system.

"PeerBlock is a new version (aka a "fork") of the popular PeerGuardian 2 software. It blocks "known bad" computers from accessing yours, for example governments, corporate entities, and those flagged for anti-p2p activities. PeerBlock maintains the functionality of the original PeerGuardian 2 program, but includes fixes for various issues that remain unaddressed in the latest (~3 year old) version of PG2.

The Peerblock application has a filter called "Bogon" Block list 

If using PeerBlock and the Bogon block list, this will stop the VPN from working - because the Bogon filter contains internal network IP's such as 10.0.0.0/8 for example.

PeerBlock will automatically allow your local network, gateway, DNS & DHCP, but block the DHCP, DNS, Local IP from the VPN network.

At this point in time the solution to resolve this is to disable Bogon Block list.