Blacklisting IP ranges from VPN access

 How can I blacklist an IP range from the VPN connector?

Someone is attempting to hack my VPN connection (through TMG 2010) from Amsterdam.  They have not gotten through the Authentication, but my logs show multiple attempts on multiple days. 

I'd like to block a range of IPs from the VPN connector on the TMG server, but can't find were to do it.

Any help would be appreciated.

Thanks,

Chris