I bought another USB to RS-232 converter. The first one cost $25, the later one cost $19.95 and it works! Seems you can pay too much for a USB to RS-232 converter.

I am firmly of the belief that MCS Loader is time sensitive and it is pot luck whether the converter you buy has a short or long internal delay. Both the converters I have tried claimed 1 Mbps throughput so raw speed is not the issue.

The one that worked came from Electus, part number XC4834. The package is labeled GUC-AD9.

HTH
BrianT