What is your Preview window size. I think there is an issue where may need to try a smaller or larger size.
I found this below in another thread...that was back in Nov and I'm not sure its been fixed.
"as mentioned in last nights tutorial. There is an issue when you make the preview too large.
Try drawing a secltion box (Shift left clik and drag). If the box starts where your mouse is , then you have a good size resolution, if the box starts someplace else, you wont be able to select objects as expected.
On i am using resolution like 1100 x 800, depends on your system. experiment unti you get it. A future release will fix this"
