WordPress MU

I deleted a bunch of test users in my WPMU+buddypress install and now I am trying to register new users using the same email addresses. However it gives me the error:

'That email address has already been used. Please check your inbox for an activation email. It will become available in a couple of days if you do nothing.'

Is this an error or is it supposed to do this? At the very least. the message should probably be different I think?

Also, how do I release these email addresses for use again? If its from the database, which records would I delete? (Want to make sure I do not mess up the database)

Thanks.

Ok, I see the wp_signups table. If I just delete records of deleted users from this will this cause any problems?

Also,

should these records not delete themselves when a user is deleted in WPMU?

also check this thread: http://mu.wordpress.org/forums/topic.php?id=11453