[DoctorOhh]

This is strange. I run calibre portable which is 32 bit on my Windows 7 box. I just installed Calibre 64 and like virtually every other person out there it works fine. All covers in the GUI and the viewer are as expected.

@PeterNL and @claudeb One thing to try is to return to completely virgin default settings. One way to do this is to exit calibre, rename your calibre settings directory then start calibre. All of your calibre settings will be recreated as a new install (uninstalling and reinstalling does not do this).