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BetterRed Sorry for the late answer. I've installed Calibre Portable in the USB3 HD and copied the library in there. The problem is the same. I've to wait more than 30 sec for the metadata editor to move to the next book

The problem is the same even if I use a different PC with win 7 64 bit( I don't have a PC with win7 32 bit so I don't know if that maybe a issue).
I've set the environment variable on my main PC (many many thanks for the detailed explanation !!!!) and the problem is solved