Can't Login to WordPress Subdomain

Hi!
I’m new to WP and have basic knowledge of html and php.
I’ve got main domain http://www.seedmedia.co.za and in its sub folder http://www.seedcorporatemedia.co.za

Because I’m modifying the look of the sub domain (both use same theme), I decided to do a separate instal of wp in sub domain folder linked to its own database (imported from an earlier version of http://www.seedmedia.co.za).

Trouble is that when I try login using http://www.seedcorporatemedia.co.za/wp-login.php it rejects new username and password and bounces me to wp login for main site.

Any pointers would be greatly appreciated.

Kindly,
Warren