TMG network Card doesn't work properly

Hey guys.

I have problem with my TMG network card.

my server (TMG) has two network card, LAN and WAN.

LAN: 192.168.1.2  SM: 255.255.255.0   DNS:192.168.1.1

WAN:10.0.0.10     SM: 255.255.255.0 GW: 10.0.0.10 (which is my router that connected to Inertnet)  DNS:8.8.8.8

Clients cannot access directly to range of WAN, except persons who have full access internet (secure NAT).

I monitor my internet connections (CMD: ping) and some times I get"Request time out". When I check connection between TMG and router I get "Request time out"

when I disable WAN Network card and after some second enable it, it work properly and it pass traffic again.