List Select Error

When trying to create a new feed, I am able to select the list that I would like to add subscribers to in Constant Contact, then I can map the fields to add, but when I click on Update Settings I receive the error message “There was an error updating this feed. Please review all errors below and try again.” and next to the list selector I receive an error “Validation Error: this field is required.” The list is selected prior to clicking on the Update Settings button but I am unable to create a feed no matter what I try. Please provide instructions on how to successfully create a feed. Thank you!