This is just SO strange. I'm sure I'm missing something obvious, but I am at a loss to figure it out.
I've been trying to create two new websites using Drupal. I find it just perfect for what I'm trying to do -- until this weird happening.
Both sites had the Category module working. And working well. I was trying out different modules on each (both sites are early in development). Some did what I wanted, and some I tried and gave up on because they were overkill for that site or because they didn't provide a function I needed. So the modules on the two sites are somewhat different. But the Category module definitely was what I needed for getting each site organized well with good menus, etc.
Suddenly, on one site, I can't change or add any content other than containers. If I do, the field "Container" in "Category Information" is blank. Nothing to select, and there's always an error message if I try to submit the page. Essentially, I can't touch the content that's there, and can't add new content.
First thought: I must have installed some module that didn't play well with Categories. So -- I thought I'd start over with a fresh Drupal on another server as a test, and added only Drupal (4.7.0 -- it comes with the hosting service as an auto-install) and Categories and Views. I did the install, created a container, and ... same problem. I then did an upgrade to 4.7.2 and ... same problem.