ENDIAN Firewall - Proxy issue when using MultiWAN

Hello,

My Setup:

Hardware:
Pentium 3.0GHZ Dual Core CPU
4GB DDR2 RAM
320GB SATA HDD 7200RPM

40 to 60 Users accessing the machine concurrently.

Endian is configured:
1- With two red interfaces, (1 Intranet and 1 Internet)
2- Routing policy rules are used to properly route the traffic between both interfaces
3- Transparent proxy is enabled, with content filtering and local authentication

The issue is:
1- After 20 minutes or so of usage the box suddenly stops web browsing traffic
2- The user is able to logon to the proxy and is authenticated properly
3- The webpage he/she is trying to open never loads, the indicator never finishes spinning and there's no error message displayed
4- All traffic specified to bypass proxy is working properly
5- I either have to reboot the box every 20 min or so, or I have to disable one of the interfaces, then everything runs smoothly

I believe this is a proxy issue, anyone facing something similar?

Please assist!