Calibre portable 2.50 issue

Hi,

I've just upgraded my portable installation from version 2.0 to 2.50 (last version, yes I've missed version from 2.00 to 2.50..:D).
The problem is that the last version doesn't recognize my Nook simple touch. It's not a pc related problem because 2.0 version it's ok. Some tips ?
I use a windows based PC with version 8.1 installed.

Thanks