501 looses registration every 24 hours

I have a 501, that was working fine while my Trixbox was on the LAN. I moved the Trixbox to a different network and now my 501 looses its registration every 24 hours. If I reboot the phone, it registers, and everything works great. However, the next day, at the same time when I look at the phone, or try to make a call, the little line phone indicators are white, instead of black, and when I check the registration status in the phone, it says the phone is not registered.

Has anyone run into this problem or know what might be wrong?