Entering a Manual Donation with a future date causes a critical error when viewing Donations >> Donations. This is because the future date gives the Donation a post status of "future", and GiveWP doesn't handle this well.
The workaround is to either delete and reenter the donation with a current or past date, or edit the donation's post_status to PUBLISH.
When in wp_posts in the database, search for anything with post_status of "future". Find the donation and change that to "publish"