Hi @burnham-phil-gma,
Using the same name as a previously deleted invitee does not affect a user's ability to log in. This error can occur if your current subscription reached the maximum number of billable users allowed. For example, QuickBooks Online Essentials allows up to 3 billable users, so inviting a fourth one would lead to this issue when they attempt to sign in. Take a look at my screenshot.

If you’ve already maxed out your user limit, you'll want to consider upgrading to a higher plan to expand it. Otherwise, I recommend contacting our live support team. They can securely look into your account and conduct a series of tests to resolve the error. Here's how:
- Click Help or ? icon in the upper-right corner of your QuickBooks dashboard.
- Go to the Search tab.
- Type in your concern, then press enter.
- Click Contact Us.
- Choose between Chat with us or Have us call you.
If you have more questions, don’t hesitate to reply.