Thanks John. That's kinda what I was thinking....but.....
The original PG USB disc always had the drive letter F:....new 500GB one is called G:
I also assumed that if the PG drive was not connected Windows would issue F: as the first available label....but Windows skipped that and calls the new drive G:?
I could probably use Disc Manager in Windows (7 - 64bit) to force the G: disc to take the label F: but don't know whether that would be the right thing to do.

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