Hi @Semidivine, welcome to the Asana Community Forum!
Just to confirm, do you have a Workspace or a Organization? Please note the option to invite Guests is only available for Organizations.
If you have an Organization and the users have an email domain connected to your Organization, they would need to leave the Organization and then you can re-invite them using a different email address. They can create a project with all their tasks so you can easily invite them to the project when you add them again to the Organization as Guests.
However, if you have a Workspace, I recommend you to convert it to an Organization.
I hope this helps! Let me know if you have any other questions!