MyGuestlist needs certain permissions from Facebook to work correctly.

If you change or update the permissions you've granted the MyGuestlist Application on Facebook, you might need to re-link your Facebook account with MyGuestlist.

Possible Reasons

1. You removed a permission specifically for the MyGuestlist Application on Facebook.com
2. You changed your Facebook Privacy Settings, including changing who can view your timeline, status updates etc.

If any of these changes occur, then MyGuestlist will prompt you to re-link your account.