What kind of controller is it? if it is an MXe than there could be an issue with the LAN interface, when the system is rebooted it works again for 15 minutes or so. You can use a workaround by logging in with putty raw 2002 an give command "period 900,mips_reset", this wil reset the LAN interface every 900 seconds. But you have to replace the hardware to fix the issue.
Gr. Mark