One Last Update.
(see previous posts for descriptions of each router)
Router 4 (supporting 2 public IPs), running the latest firmware 1.08B51, continues to crash every 18-24 hours. However, with the new firmware, it reboots itself after the crash for a total of about 3 minutes of downtime each time. At least we don't have to call someone in during the middle of the night.
I took one of our newer DSR-500s running firmware 1.08B33 and programmed it to replace the older DSR-500, Router 3, (firmware 1.03) that we've had running for many months. This network supports a single public IP, up to about 20 computers, no firewall rules or special routing - just straight internet access. The newer router ran fine for 2-3 days then crashed twice in an hour. I thought I had narrowed it down to multiple public IPs being the cause, but after this experiment I'm not so sure.
I attempted to program the older router to replace the newer one that crashes every 18-24 hours, but the old firmware does not appear to allow routing from more than one public IP.
I also discovered that when attempting to program the older firmware (1.03 and 1.04) in Internet Explorer 9, many of the configuration screens do not display correctly. But they display fine in Chrome.
So, I have requested an RMA for all 3 of the new routers.
In case any one else is having issues, the serial numbers for my units are:
QB9V1D3000003
QB9V1D3000014
QB9V1D3000019
We also purchased a fourth at the same time, serial number QB9V1D3000032. That one was sold to a customer with a very small/simple network and appears to be able to handle the load.
Thanks for your help.