Once again my contacts won't sync from CRM to Campaigns

Once again my contacts won't sync from CRM to Campaigns

I am trying to sync another group of contacts from CRM to Campaigns. I don't understand why it's not working. Attached is a screen shot of the error message I'm getting.

Do I need a new key every time I sync a group of contacts?

This is very frustrating.

AND
I am trying to send a second email to people who have not opened a previous email. I tried creating a new segment but I can't get the criteria right. Why isn't it possible to select individuals within a segment and send to them. There are already boxes to check next to the contacts.

Thanks.