Windows 8 Tab Key

I've been using this awesome software for quite some time on Windows 7. I typically use the Tab key to advance to the next image, but am receiving this popup when hitting tab under Windows 8 64bit. I tried the latest version under Windows 7 64 bit, and tab works as expected. Any idea what's causing this? Thanks!
FastPictureView - Thumbnail View (Tab Key)
The Thumbnail View feature needs a bit more developement and has been disabled in this build...