Hey there thanks for the post. I will reach out via email to get more information on this since this deals with account-specific information.  Please be on the lookout for an email from support@lucidchart.com.

For others encountering this issue if you are receiving this error as described above what happened most likely is that an account was created for that email at some point. I recommend trying to log in with that email and deleting that account. You can request a password reset here if necessary. You should then clear your cache and cookies and attempt to change your email again. This should do the trick!