VPN Error 619 from DMZ

Hi all,

When i try to connect to my VPN  (PPTP on a 2008R2) server from DMZ I got 619 Error.

In TMG 2010 logs i got this:

Result code: 0xc0040017 fwx_e_tcp_not_syn_packet_dropped

Status: A non-SYN packet was dropped because it was sent by a source that does not
have an established connection with the Forefront TMG computer.

What could be wrong?

Thanks!