Don't use the cheap USB to Serial cables -- especially those with the Prolific chip. They're unreliable because they don't deal with the voltage difference between USB and Serial and it thus becomes a crap shoot if the USB's voltage tolerance when combined with the device's voltage tolerance (in this case the RC210) happen to match just enough to let the device work.
We've had very good results with the Gigaware cables (such as the ones sold in Radio Shack). They're expensive (about $40) but they do have a transformer that adjusts the voltage and they work very reliably with our software (and other's too!)
Created : 2012-12-16 10:46:42, Last Modified : 2012-12-16 12:47:34