This is a Microsoft Windows driver bug with some 64GB CF cards. Sonnet is working with Microsoft to resolve this issue. (64GB and 128GB CF cards work fine with Qio and Qio-CF in OS X.)
A partial list of cards Sonnet has tested:
Patriot Pro CF 266x 64GB/128GB card is recognized under Windows
Lexar Pro 1000x UDMA 7 64GB/128GB card reports itself as 32GB
SanDisk Extreme Pro UDMA 6 64GB/128GB card reports itself as 32GB