MightyOhm.com

I found this:

FT232BM or FT245BM device hangs randomly during operation under Windows XP
This is not caused by the driver, but is a hardware compatibility problem. Some newer USB 2.0
hubs and host controllers can be susceptible to noise and can cause random device failures. This
can be overcome by fitting 47pF capacitors to ground on the USBDP and USBDM lines on the USB
connector side of the 27W series resistors.

So it looks like it is a hrdware issue. However, I have tried many 2.0 hubs (cheap to fairly expencive,) but have not found any that work (if anyone know's of a hub that works, please let me know.) I have looked for a 1.0 hub, but it looks like they are no longer available.

So I'm planning to add the 47pF caps, but I'm not sure how to do that. Do I add it to the relay board or to the hub? and to which lines. Assuming it's the relay board, I'm gussing that it is the two usb lines that are not ground or +5. Can anybody verify?

The 47pF capacitors go as close to the FT232 or FT245 chip as possible. That means they go on the relay board, next to the IC.

You want to solder them from D+ and D- to ground. I would use a surface mount capacitor if possible, thru hole components might have too much series inductance.

Take a look at the datasheet for the FT232, it shows the pinout and I think it might show the optional capacitors as well. I know they are shown in some FTDI example circuits on their website.