unable to 'manage fields' in CCK

When i create a new content type and then try to 'Manage fields' it takes me to the Content management page where I see the following menu options...

Comments
List and edit site comments and the comment moderation queue.
Content
View, edit, and delete your site's content.
Content types
Manage posts by content type, including default status, front page promotion, etc.
Forums
Control forums and their hierarchy and change forum settings.
Newsletters
Manage newsletters and subscriptions.
Post settings
Control posting behavior, such as teaser length, requiring previews before posting, and the number of posts on the front page.
RSS publishing
Configure the number of items per feed and whether feeds should be titles/teasers/full-text.
Taxonomy
Manage tagging, categorization, and classification of your content.

I am able to see the content type in the content type list, but unable to delete it or manage fields, both of which bring me back to the above page. Thsi issue started since the time I recently shifted to Drupal 6.16. from Drupal 6.15.

Please help...

Thanks
VR