UPDATE...
It looks like a win 7 issue.
If I plug it into a server ( server2012 ) It works fine.
However that still leaves questions about why ONE of the TWO boards works whilst the other doesn't ?
Normally I am pretty darn good with computers and troubleshooting so if anyone has any clues at all or even a stab in the dark as to what could cause this then thank you in advance.
USBSER.SYS was replaced ta some point and identified as the probable cause.