warning: Invalid argument supplied for foreach() in \content.module on line 1284.

This occurs when I attempt to create a forum topic.
I installed a clean Drupal 6.17 with views-6.x-2.11, panels-6.x-3.5, ctools-6.x-1.6, cck-6.x-2.7. All is well.
I then installed advanced_forums-6.x-2.0-alpha2, author_pane-6.x-2.0-alpha2, All is well.
I then installed nodecomment-6.2x-2.x-dev (head as of 06/07/2010). All is well.

Now here is where it goes bad.

In content types, I changed Forum topic-> Node type for comments from -- Drupal comments -- to Forum topic, and Comments from -- Drupal comments -- to Comments.

I got a problem detected and checked the status report :
# Content type Comment is a comment type for itself, but there are no other content types using it as comment.
# Content type Forum topic is a comment type for itself, but there are no other content types using it as comment.
So I then changed the content types back, cleared the caches, etc. Went to Forums, Selected the Forum, click on New Topic, and I now get the above error.

My Forums are simple a Container which holds a Forum.

Its obvious I'm missing something or confused when dealing with content types and nodecomments. But the only thing I did was change the types, and then change them back.

BTW, do a google on this error, and there are hundreds of sights with this on their front page! Scary.