I faced a similar problem. But after a bit of trial and error I understood a work-around. I tried to share the notebook via EverNote desktop app for Windows, but it didn't work. Then I tried via Evenote Web version and initially it didn't work, but later I figured out a way.
@Drold: When you click on the share button for the notebook, in the drop-down menu they show "Suggested chats" drop-down with names of people in your organization/frequently contacted. I thought that these were my options I had to send to and I clicked on those people and clicked "Send". But the people confirmed that the notebook had not been shared.
Then, after a bit of trial-and-error, I realized that when you click on Share button, then in dropdown, first there is a "Suggested chats" section... but below that there is "Suggested Users" section.. so when you type the email address of that person with whom you want to share the notebook, then either just type the entire email and click share or else select the user populated only in the "Suggested Users" section (not the "Suggested chats" section).
Do give it a shot and let me know if this works for you.