Drupal pages disappear after changing access permission to attachment

Drupal 5.20. 

I decided to create a certain user-group of people who would have access to the attachments posted on different pages in the site.

When people from that group would login, a special menu would appear with the links to the pages with attachments.

Nice and easy. I am not a great Drupal-er, but the little knowledge I have is solid, I believe.

All was working fine, I tested the solution a few times on different browsers. Till I created the first user and let him start using it. 

Page not found, he told told me that he gets on the links with the pages with attachment. 

I thought that he might be doing something wrong. Then I created a new user account giving it same permissions. Nope. Page not found. Then I logged with the initial account that worked just a few hours before. Same page not found.  

I could see the pages as administrator, but not a a member of that user group. So I thought that the file upload module user permissions were in question. They were not. I checked all possible permissions, many times. 

Then I realized that even anonymous users can't see these pages with attachments. 
So I removed the attachments of one of the pages in question, but they were still invisible for the public! 

Then I realized that ANY new node I create, new post, be it blog or whatever, becomes 'invisible'. i.e., access is denied for any new page to anonymous users, although properly published etc.

Weird, weirder then weirdest. 

Users? Access permissions? What went sooo wrong from one moment to the other? The update that I made a few days ago to Drupal 5.20? 

I was searching for a possible, logical explanation going in circles: access control, forums-user groups... 

Till I finally I found this little post  who pointed out that in such weird situations one should always rebuild the node_access table (/admin/content/node-settings). 

That was it. That was the little button that I was searching for 12 hours (incl 5h sleep). 

I pressed the button, confirmed my decision and yes! All was back to normal.  

I wrote this whole story just in case someone else (or me) comes in similar position.