basic login/registration problem

Have set up WPMS via subdomain option. Can create a new site no problem. Can also create a user via the network dashboard but I see no option to assign the new user an access level – subscriber, author etc. Can delete this user with no problems subsequently.

Next – in Network Admin I have allowed new user registration in Settings (though not at this stage new user site creation).

When I register a test new user via the main site (the sub site redirects to the main site registration) I get the activation and confirmation emails. All seems OK, but the second email directs me to: http://mainsite.com/wp-login.php. Following this link allows me to log in with the new user name & password but does not show the site itself – it simply takes me to a dashboard.

When I delete this new user via the network dashboard, it deletes it accordingly and also deletes it from wp_users in phpmyadmin in CPanel. BUT I cannot re-register the same user name and email address via the main site – I get an error message that the name/email address is taken and to try back in 2 days.

Tried registering a second test user with different username/email address – but now the activation & confirmation emails do not arrive.

Where am I going wrong?