Problem/Solution not yet understood or known

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Things we've tried so far.  ---  (8/8/2)

1) Reinstalled drivers.
2) In Device Manager we can see COM3 come and go when converter "re-plugged".
3) Downloaded latest Mapsource Ver 4.09

To be continued:...

Background info found on-line:

SONY VAIO --- problems?

From intel.com/support (8/8/2)
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Q. It has been reported that the USB ports 
on the Sony Vaio machines are unreliable? 

Actually this is a feature of the Vaio. 
Only 2 of the three USB port can be active at one time.  
In particular, if the two ports on the PC are in use 
the front one becomes disabled if (say) the USB floppy 
is inserted into the port expander USB port.  
Therefore, we recommend not using the USB port 
on the Vaio port extender module.

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