This is not a question, but a issue that has been soved that might be usefull to someone else to avoid pain.
Windows Vista 32 bit
The initial problem was that my communications on com port 2 (my VFD connection) is always perfect with no issues, but as soon as I turn on a VFD (variable Frequency Drive) the communication between the PLC and a computer instantaneously and permanently stops until such time the VFD is stopped (not powered down) and then the communications can be re-established to the PC.
I have tested out just about everything I can to make sure that the answer is correct and not accidental.
1) I have an RS485 with termination using Modbus RTU protocol on com port 2, 19200 com speed 8,2,none connected to a FUJI brand VFD
2) I have com 1 at the default 232 connection to go to the computer using a USB to serial adaptor the has been in constant use for 2 years and never had any trouble (cable from “cables to go” the model is 26886)
3) I have tried shielded com wire both grounded and ungrounded. (no help)
4) I have altered the output carrier frequency of the VFD (Higher the carrier frequency on a VFD the more electrical noise is generated) (no help)
5) I have tried with a motor connected and not connected both with and without grounding. (VFD wiring to a motor can act as an brodcast antenna) (no help)
The answer is the USB to serial cable that has and does work when no VFD is running is the root cause of the condition.
I have other USB to serial converters and have replaced the original with a metal cased USB-COMi-M that was purchased from www.byterunner.com for $59 and when using the different USB to serial adapter everything works smoothly with no issues under all conditions. I have also run direct to a 9 pin serial port with the standard programming cable and all communications are perfect with or without the VFD running. I think I can correctly and safely say that nothing in either the Unitronics hardware or software is to blame for the troubles I have had.
It has taken me most of a day to figure this out so I figured I would pass the information on since it might be useful at some point in the future when someone else has a similar problem.