I was using calibre portable to generate my catalogs, but it seems it became too big and it failed on a memeory error. I switch to calibre 64 and it went again OK.
the only difference I see is the width of the thumbnails of the covers.
Is it possible that I can go wider in width with the poartbale version than with the 64 version. if I add (in 64) a value higher than 2 inch things doesn't change anymore... the same value in the portable version although gives wider thumbnails - it is easily seen in the thumbs.zip file as well which is 30 % smaller with the 64 version.