Thanks for trying to help!
Here is the message I get when trying to sync ( I changed the options to what you recommended and get the same answer) - itunes could not sync photos to the ipad "_______" because your Aperture Library could not be found. Open the preferences window in Aperture to enable the preference to share previews with other applications.
Denise, after enabling the sharing option force the creation of previews. Select all photos that you want to share and use the command "Photos > Update Previews".
Then quit Aperture and log off and on again, to make Aperture update the preferences file. Only then try to launch iTunes again.
"_______" because your Aperture Library could not be found.
Where is your Aperture library located? Is it on your internal system drive or on an external volume?
What is your Aperture version and MacOS X version?