Thanks for those details! I think I know what's going on here.
Emma uses the email address as the unique identifier for your contacts. So, if you're attempting to change an email address to a version that already exists in active status somewhere in the account, it will not let you change that error address. It's likely that you have the correct and incorrect version of several addresses in your account.
You can search your audience for the address you're trying to update that to and make the necessary revisions to that contact record instead!