I looked at this some more. Assuming you have many new users trying to register from the same IP address, you can whitelist the IP address. To do this, go to Admin/Logs/Screened IPs. Enter the IP address into the ‘New’ box, select Allow from the dropdown menu, and then click the Add button.
When an IP address is whitelisted, new users will not be prevented from creating accounts with that IP address. One thing to consider is that you are opening yourself up to spammers from this IP, so whitelisting an IP address should be done with caution.