Hello @michelle,
Welcome to the LastPass Community!
I apologize for the inconvenience this is causing you. Do to this is a public space I can not ask you for the email for the affected user but it might be possible that the user have a personal account which will be outside the business. Verify if the user is able to make a delete account process and then try again to activate the user. You can find the steps the user needs to follow here: https://support.lastpass.com/s/document-item?language=en_US&bundleId=lastpass&topicId=LastPass/delete_your_lastpass_account_dont_know_mp.html&_LANG=enus
If the issue persists, please create a ticket so we can give you a more personal and not public support.
Kind Regards,
Alejandra
LastPass Support