If you're getting an error message when trying to add an email with special characters—like an apostrophe—into your address book, it's most likely it is because you are copying and pasting the email into the field. When you use a copy and paste with an email address with special invisible characters of the UTF attributes can cause a problem.
All you have to do is manually type out the email address. This will get rid of any invisible characters that were copied over and allow you to save the contact email address.
There also might be an extra space at the beginning or end of the field that is causing the alert. Try deleting all unneeded spaces and see if that resolves the issue.
If that does not work, try refreshing the page and typing the entire email address in lower case letters.