Hi again,
On my last trip to site, I upgraded the systems to LV8.5.1 and NI-RIO 2.4. Everything is still working fine (it's been about 2 months since we've set up the VLAN which is what first solved my problems). I should really take my systems off the VLAN to see if the dreaded "TCP/IP stops working wothout reason" problem comes back. That way we would know if it was a bug between NI and all the multicast traffic and if that bug is really fixed. If this happens, I'll make another post to report my findings.
Thanks to everyone who's helped..
Long John Martin.
P.S. The RTOS in the cRIO definitely replies to the ping command (as long as it's talking).
