What OS X are you using?
I did some googling and found this:
https://discussions.apple.com/messag...ageID=10634835
"Mac OS X
Sony released an official Mac OS X client for the Reader with the release of the PRS-300 and PRS-600. It is reported to work with the PRS-505, PRS-700, Reader Pocket Edition and Reader Touch Edition. *The software works under 10.6 Snow Leopard, but only under 32 bit mode as it relies on a kernel module that does not currently support the optional 64 bit kernel.*"
Also check out:
https://www.mobileread.com/forums/showthread.php?t=63043
That solved it."
https://www.mobileread.com/forums/showthread.php?t=63043
"For mac users: do not boot into 64-bit mode (holding down the 6 and 4 on the keyboard while booting).
The option to boot just the application in 32-bit mode is not available when you click Ctrl-I.
Hope this helps someone."
So are you using 64 bit SL? Boot into 32 bit then? Mine is 32 bit.
Btw, people have said that Sony software is buggy. I think it's ok but at the same time I only use it to buy books. After that I drag drop books onto the reader. Mostly if I have to use a software I use Caliber.