People cannot register! WHY?

Hello!
I created a new forum. I already have 2 registered Users, my mods.
Now other people tried to register...but they recieve a message, that either the username is already taken or the email adress has already been used. But neither is the case!!
What's wrong there? What can I do?
I'm absolutely confused. Can anyone help me?

did they get a notification in the email... they need to check their
bulk mailbox

me too..have a problem like that..no notification recieved via email..for the past 2 days now...can someone help me out..?

If someone registers and does not recieve the confirmation email for whatever reason (email filters, etc... for example), and they try to register again with the same data, they will get the error message as described above.

The reason is that their status is "pending" - you can manually activate accounts in "Users & Groups / Users / Inactive Users". You should find their accounts there.

Be sure "New accounts activation" in "Users & Groups / User Options" is set to USERS, if you want that users confirm their account themselves by default.